#help-49

1 messages · Page 261 of 1

wraith dirge
#

wdym

last slate
#

dude like

coarse wing
lavish venture
#

what?

wise flicker
#

There are 18 slots, choose 4 C(18,4) and then arrange A729 4!

wise flicker
last slate
#

p(32,14) is the set of 32 characters in premitations in the form S = {32}

So then S x S-1 x S-2 x … x S-31

lavish venture
wise flicker
coarse wing
#

alr ima take a nap

wise flicker
last slate
#

I genuinely hate this

lavish venture
last slate
#

Bro what do they want from me

lavish venture
#

or are you doing some sort of other science

last slate
coarse wing
#

is this breakdown

last slate
#

im gonna continue majoring in stem

wise flicker
coarse wing
#

@prime hornet !!!!!!

#

help him

prime hornet
#

||honestly, I hate this sort of counting too sadcatthumbsup||

coarse wing
#

my brain overloaded

last slate
#

this is universal bruh

hallow crane
last slate
#

i love math but this tests your limits

coarse wing
last slate
#

id rather do physics every hour of my life than this

coarse wing
wise flicker
last slate
prime hornet
coarse wing
#

yeah

#

f#$^ counting

wise flicker
#

Ts how pnc is

last slate
#

lowkey i wanna hop on vc for this

hallow crane
#

Invariance, monovariance,etc are far superior forms of combi

wise flicker
#

Take him @hallow crane

coarse wing
hallow crane
wise flicker
wraith dirge
hallow crane
wise flicker
coarse wing
wise flicker
#

Lmao why

#

Its repeated letters

coarse wing
#

$\binom{8 + 3 - 1}{3 - 1} = \binom{10}{2} = \frac{10 \times 9}{2 \times 1} = \mathbf{45}$

grand pondBOT
coarse wing
#

leon

#

think

wise flicker
#

Hmm.. usually we jus divide by no. of repeated

coarse wing
#

aight

#

cya

wise flicker
#

@leon you there

last slate
#

yes

wise flicker
#

K then 4!×C(18,4)

#

What is it

last slate
#

i dint understand what you did there

coarse wing
last slate
#

there are 4 letters that must exist in the mix,

#

just calculate how much you can rearrange them

coarse wing
#

let me turn this channel notification off

last slate
#

which is 4!

#

And then

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idk

wise flicker
#

Length of password was 18, we choose 4 spots for those letters then arrange at those 4 spots

#

Total spots were 18 so C(18,4)

last slate
wise flicker
#

Combinations

last slate
#

what is the goal here

wise flicker
#

To choose 4 spots

wise flicker
last slate
wise flicker
last slate
#

differential equations is easier than this

wise flicker
#

You get P(18,4)

last slate
coarse wing
#

@last slate do you truly understand how permutations and combinations works and its theory.

wise flicker
last slate
coarse wing
#

because if you dont get it you cant understand what we are explaining

last slate
wise flicker
coarse wing
wise flicker
last slate
#

aw man

#

yes

wise flicker
#

You got answer

last slate
coarse wing
#

if its too hard or you need to revise you can talk to your professor

last slate
#

ive been self studying my entire career

#

Except for one class where the professor gave a shit and had some conscience

coarse wing
# last slate my professor doesnt explain well

This video tutorial focuses on permutations and combinations. It contains a few word problems including one associated with the fundamental counting principle. Permutations are useful to determine the different number of ways to arrange something whereas combinations are useful for determining how many ways to combine something when the order ...

▶ Play video
#

luckily i saved this in my playlist

wise flicker
coarse wing
#

😆

coarse wing
last slate
#

But like

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can i still get an explination for that question

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This

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what does P(18,4) do

coarse wing
#

eventually you will found out the explanation by yourself

last slate
#

okay

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thank you

coarse wing
#

yw

last slate
#

but

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i already know what it means to do a permutation and combination

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but my question was why do a permutation like that one in the first place

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why

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im saying why

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cooked

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<@&286206848099549185>

void lichen
#

are you asking why you need to do a permutation here

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this is your original problem right

last slate
#

whats the set of 18

last slate
last slate
void lichen
#

which is given

last slate
void lichen
#

im pasting the problem again for my reference

#

each valid password

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will have to be 18 characters long

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now, the restriction states that it must contain a, 7, 2, and 9

last slate
#

yes

void lichen
#

now let us look at what the first character of our password can be

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it can be any of the 4 characters

last slate
#

yea

void lichen
#

we must

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then the second characrter can be any fo the 3

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because we cannot repeat characters

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so we have 4, 3, 2, 1 which is 4!

#

the first character can be a, 7, 2, 9
Suppose we pick a
then second can be 7, 2, 9
then we pick 9
third can be 7, 2
we pick 2
fourth has to be 7

last slate
#

?

#

i mean 4 slots

void lichen
#

yes of the 18 slots we want four to be the MUST CONTAIN characters

#

rather

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the first character can go in any of the 18 slots

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second can go in any of the 17 slots

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third can go in any fo the 16 slots

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last can go in any fo the 15 slots

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now these four characters can be arranged among themsleves in 4! ways

last slate
#

is that what youre saying

void lichen
#

yes

last slate
#

okay i agree

void lichen
#

so we have 18 then 17 then 16 then 15

#

and then these four characters can be arranged in 4! ways

#

okay now what is a permutation it is n! upon (n-r)!

last slate
void lichen
#

the second character '2' can go in any of the 17 places

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because a took up one place

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accordingly, the third character '7' can go in any of the 16 places

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now, the fourth character '9' can go in any fo the 15 places

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the answer is for why it's 18 p 4 is understanding it like 18 times 17 times 16 times15

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first goes into 18 slots

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second 17 slots

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third 16 slots

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fourth 15 slots

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which means 18 times 17 times 16 times 15

last slate
#

Yes but how does the permutation look like for that

void lichen
#

okay so

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a permutation is

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npr which is n! upon r!

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here n = 18

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and r = 4

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so 18! upon (18-4)! would be

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18! upon 14!

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which is actually just 18 times 17 times 16 times 15

last slate
#

but youre doing the premutation on the 18

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which is like what an empty set?

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or what

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like

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what are you putting in slots of 4

void lichen
#

we are putting the four characters in 18 slots then 17 slots then 16 slots then 15 slots

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so we have picked

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4 slots

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do you get that

last slate
#

yes

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i just dont get how P(18, 4) solves it

void lichen
#

p(n, r) calculates the number of unique arrangements possible when choosing r items from a set of n items

last slate
#

you’re doing a permutation from the set of 18

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yes 18 what

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what 18 items are we taking

void lichen
#

18 places

last slate
#

so places

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okay

void lichen
#

18 different places where can put the characters in

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out of which we just want to put the characters into 4 palces

last slate
#

sure okay

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and then in each place the letters can be arranged 4! Times

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So thats 4! * P(18, 4) no?

void lichen
#

p(18, 4) already accounts for

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that

last slate
#

nevermind it aleady counts for it

last slate
void lichen
#

yup

last slate
#

ye

void lichen
#

think of it less in terms of the rigid formula npr

last slate
#

well thanks man thats all i needed to know

#

🤣

void lichen
#

cool

coarse wing
last slate
#

yeah i just needed to know wth 18 was

coarse wing
void lichen
last slate
void lichen
#

i didn't know how to explain the fundamental idea of permutations

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cool alr

coarse wing
#

@last slate you are missing the donuts

last slate
#

now time for subsets 😈😈😈

coarse wing
#

no

coarse wing
#

it

last slate
last slate
#

the one i already did

coarse wing
last slate
#

rn?

#

Sure

#

.close

midnight plankBOT
#
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coarse wing
#

bai bai

midnight plankBOT
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fossil wagon
#

anyone know how to do qn23 b and c?

midnight plankBOT
paper mantle
fossil wagon
#

which is 20.6

paper mantle
fossil wagon
paper mantle
#

okay

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so for ur B, ur question says AC = 2/5 AB

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u have ur AB so u can find ur AC

fossil wagon
wooden badger
fossil wagon
#

but how would I find two unknowns x and y coordinates?

wooden badger
#

You've been given the ratio of AB and AC

fossil wagon
#

not the coordinates?

wooden badger
#

Do yk the section formula?

fossil wagon
#

yeah

#

d = √[(x₂ - x₁)² + (y₂ - y₁)²] this right?

wooden badger
#

So you could assume the coordinates as variables and apply tht

fossil wagon
wise flicker
wooden badger
wise flicker
wooden badger
#

Oh

midnight plankBOT
#

@fossil wagon Has your question been resolved?

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severe grail
#

I need some help

midnight plankBOT
severe grail
#

what is it asking?

obsidian anvil
#

for example if the average (mean) score for an exam was a 70 and the standard deviation was 8, the score that is one standard deviation from the mean is the mean + 1*std (standard deviation)

#

the score that is 1 standard devation below the mean is mean - 1*std

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does that make sense

severe grail
#

do we add 1 to z and solve the equation

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for the first question

obsidian anvil
#

the expression you would be using is

#

$\mu \pm \sigma$

grand pondBOT
obsidian anvil
#

where mu is the mean and sigma is the standard deviation

severe grail
#

is it ok to use x bar?

obsidian anvil
#

If a score is one standard deviation above the mean, you add one standard deviation to the mean

obsidian anvil
#

you dont need to necessarily use variables to answer this question

obsidian anvil
severe grail
#

ohhh ok I think i get it now

#

basically

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a higher z score means

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more area on the curve

hushed mauve
#

a higher z-score means you are further along the curve (as in further to the right)

#

you can only have an area if you're calculating P(x < or > z-score)

severe grail
#

P(x < or > z-score)

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I dont understand this

hushed mauve
#

I thought I made it simple enough

#

basically, if you're looking for a range of z-scores (like P(x > 1.5)) then yes, you will get an area

#

otherwise you're only getting one point

severe grail
#

because thats what is written in some of my problems

hushed mauve
#

just a var difference, but sure

midnight plankBOT
#

@severe grail Has your question been resolved?

midnight plankBOT
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wind oxide
#

consider a $7$ digit number $abcdefg$ such that $d$ is the greatest digit and digits towards the left and right of $d$ are in decreasing order (from left to right). then the total number of such numbers in which all digits are distinct

grand pondBOT
#

rak³en

wind oxide
#

wait a minute

#

9c7 * uhh

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36?

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hmm does not seem to match

slow thorn
#

i think its like 1234321

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oh from left to righ

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mb

#

so like 3214321?

wind oxide
#

its alr

wind oxide
#

yes btw thats what i am thinking

wind oxide
#

OH

formal orchid
#

This is very similar to that AMC 10/12 problem.

wind oxide
#

9C7 6C3

#

IT MAKES SO MUCH SENSE NOW

hallow basin
#

Lmao I have done this one b4 lol

wind oxide
#

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hallow basin
#

uh

#

already?

#

that was fast

formal orchid
#

Oki, so $7 \le d \le 9$

wind oxide
#

i am done

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🙂

formal orchid
#

DW

wind oxide
#

this was my initial approach btw but i saw the options and knew there was some pncier way

grand pondBOT
#

Erebus

slow thorn
formal orchid
#

That seems to be the case.

slow thorn
#

getting the same answer considering from 1 to 9

#

cant you just safely say 10C7 times 6C3

formal orchid
slow thorn
#

zero would never come to the first position

midnight plankBOT
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formal orchid
# slow thorn why so

||10C7 * 6C3|| is for all possible cases (including 0)
||9C6 * 5C2|| is for cases where 0 comes first (excluding 0)

formal orchid
#

.close

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slow thorn
#

arent the numbers arranged in descending orderr

formal orchid
slow thorn
#

yeah but the digits are already said to be arranged in descendign order

formal orchid
#

1239876

#

Is the above one not of such possibilities?

slow thorn
#

nah i think 3219876

formal orchid
#

Ahh oki

#

Then ||10C7 * 6C3|| is valid

#

Since 0 can't be first

#

(misread the question 😅 )

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twilit field
midnight plankBOT
twilit field
#

Just wanted to make sure I'm not tripping

#

all I do is find |J|

#

and set x= ( 3v-u)/10

#

where J=1/10

#

so the joint pdf id (3v-u)/(100)?

zealous schooner
#

What is J

twilit field
#

The jacobian

#

this is my formula

wooden badger
#

Ping helpers?

#

@twilit field

twilit field
#

yea?

twilit field
# twilit field

Like just want to be sure the domain doesnt affect the method, or how its applied right

twilit field
marble hedge
#

Joint Density

#

Damn
i don't know about this.

twilit field
#

.close

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odd totem
#

Ho can i draw it correctly ?

midnight plankBOT
lusty python
gusty falcon
lusty python
odd totem
gusty falcon
#

OP's question was clear enough, so i saved him the trouble of having to rewrite the same thing again

lusty python
wise flicker
lusty python
#

!noans

midnight plankBOT
#

The purpose of this server is to help you learn, not to hand out answers. Do not ask someone to give you the answer directly.

lusty python
marble hedge
marble hedge
#

If that was true

lusty python
midnight plankBOT
#

@odd totem Has your question been resolved?

lusty python
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thorny folio
#

Hello great math fellows, I need some hint regarding a numerical analysis question I have.
I'm totally lost, and confused.
Here is the question:

Considering the following iterative methods.
\begin{flalign}
x_{n+1} = z_{n+1} - \frac{f(z_{n+1})}{f'(x_n)}
\qquad\qquad
z_{n+1} = x_{n} - \frac{f(x_n)}{f'(x_n)}
\end{flalign}
Assume $f(p) = 0$ ($p$ is a root of $f$). Prove that the sequence ${x_n}$ converges to $p$ with convergency order of $3$.

I'm totally lost. The iterations look like Newton's method, but it seems one is dependent to another one. Shall I just plugin $z_{n+1}$ to the first one, and try to solve it?

In my text books states that the Newton's method has order of convergency of 2 if $f$ is linear, otherwise it's 1.

Thank you for your time and consideration.

grand pondBOT
#

idiot_max

midnight plankBOT
#

@thorny folio Has your question been resolved?

runic hamlet
#

you can try replicating the proof in your textbook of the order of convergence for newtons method

#

although your claim about that seems false

#

if f is linear then it should converge immediately

#

and it should have quadratic convergence quite often

#

but you do need more assumptions for your function f

thorny folio
thorny folio
grand pondBOT
#

idiot_max

runic hamlet
#

yes

#

<= would be enough I suppose

thorny folio
# runic hamlet yes

Much appreciate it. And any hint how to find the constant $c$ (asymptotic error const) ? and is it legal to assume $p=0$ ?

grand pondBOT
#

idiot_max

runic hamlet
#

well the classic way would be to plug in a few terms from the taylor series and work with that

#

I think

#

so try that

#

look at how your textbook proved the claim for newton

thorny folio
#

Thank you. Yes, understood.

thorny folio
# runic hamlet so try that

Thank you so much sir, really really appreciate your time and consideration. Math bless us all.🍻🤓🤘

#

.close

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#
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wispy pawn
#

.open

#

hi

wise flicker
midnight plankBOT
#

To ask for mathematics help on this server, please open your own help channel or help thread. See #❓how-to-get-help for instructions.

scenic wyvern
# wispy pawn .open

!occupied unfortunately. if you have a question, please grab an available channel

midnight plankBOT
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dusty portal
#

gggggg LALALAL (supposed to be a really dramatic entrance)

dusty portal
#

So I'm completely lost on the 2nd part of this proof...

#

I intuitively understand how it works, but I have no words for it

latent wadi
dusty portal
#

I understand it like how P(A cup B)=P(A)+P(B)-P(A and B)

#

Waaaaaaaaaait

#

Lemme draw a probablity diagram rq, just continue with what you were saying

dawn dagger
latent wadi
#

It shouldn't be too bad if they already have the intuition for the problem

dusty portal
#

ouuuuu

dusty portal
runic hamlet
#

pick a basis

dusty portal
#

{e1, e2} ig

#

For both A and B?

runic hamlet
#

ok how did you show the first part...

dusty portal
#

Ok I might be screwed

#

brb, lemme get my book

#

goddamnit

prime hornet
#

<@&268886789983436800>

prime hornet
dusty portal
#

Oh

#

I keep on seperating these questions vro 🥀

dusty portal
#

Ok I think I see what I can do here

#

And I choose basis for A cap B right?

#

aight

#

I'll see if I have any other problems with this

#

.close

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sturdy barn
#

I am so lost how to do this

midnight plankBOT
sturdy barn
#

So I think A

#

Just write the formula and add the numbers?

grand pondBOT
sturdy barn
#

W bot lol

#

For 4a. I did

#

€C=275x1+1+150+25n

#

Is that good?

wooden badger
#

Where is c and w?

wooden badger
sturdy barn
#

Uh

sturdy barn
wooden badger
#

Acc to the formula yes

sturdy barn
#

€C=275x1w+150+25n

wooden badger
#

Yesyes

sturdy barn
#

Okay so now for 4b uhhh

wooden badger
#

Tht i believe would be correct

#

Just insert values

sturdy barn
wooden badger
sturdy barn
#

Four people=100n?

wooden badger
#

N is the no. Of ppl

#

So yes

sturdy barn
#

€C=275x2w+150+100n?

sturdy barn
wooden badger
#

Yup

sturdy barn
#

Lowkey forgot but I will try

wooden badger
#

Forgot what its js calculation TT

sturdy barn
wooden badger
#

You just need to plug in the values

#

And calculate

outer saffron
sturdy barn
#

Ohhhhhhh now I know how to do these thanks

#

.close

midnight plankBOT
#
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#
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last slate
#

Hi i need help understanding the logic behind this formula

wooden badger
#

Thte ncr?

quiet grove
#

go through these

last slate
quiet grove
#

its called the stars and bars method u can check it out on yt

last slate
#

i just need someone to explain to me the intuition

quiet grove
pearl mist
wooden badger
#

Ooh the gap method

last slate
#

the amount of what

#

and does it count duplicates

pearl mist
#

maybe thats why i learnt it as beggars method

quiet grove
#

yeah

last slate
#

You would like distribute it amongst 12 people?

#

so you would have like 3 vanilla 2 glaze 4 crums and 2 chocolate

#

and you would see how many ways you can make a similar combination?

#

but then what about duplicates n stuff

quiet grove
#

this wouldnt be applicable here because the cupcakes are distinct

#

neither are the people so u cant manipulate it in the opposite way

pearl mist
#

you need identical cupcakes and different people

last slate
#

for God’s sake explain this to me man ive been trying to understand that too

#

@quiet grove

quiet grove
#

if 2 things are the same they are undistinguishable

#

2 people are not the same so they are distinguishable

wise flicker
#

Stars and bars applies directly only to identical objects

quiet grove
#

a vanilla and a glaze cupcake are not same so they are distinguishable

pearl mist
#

ok forget about 5 bucks say 1 coin for each thats more easy to understand you cant distinguish 2 coins if they have the same value

quiet grove
#

yeah

wise flicker
#

You can do this way, how many ways can you cholse flavour for 1 person

last slate
#

and what are we counting for

#

what multisets are we counting here

quiet grove
#

just like the number of solutions for x1+x2=4

#

0,4
4,0
1,3
3,1
2,2

#

this is what you get from the formula

pearl mist
quiet grove
#

(4+2-1)C(2-1)=5C1=5

quiet grove
last slate
#

just as an example like say 5

#

okay and they are distinguishable

#

now what

pearl mist
pearl mist
last slate
pearl mist
last slate
#

the whole section is titled “counting multisets”

quiet grove
#

{1,2,2,0,0} {1,1,1,1,1} {1,0,3,1,0}... etc

last slate
quiet grove
#

yaah

last slate
quiet grove
#

and the number is number of coins

quiet grove
#

because the formula u sent specifies there are no restrictions on how much can go to each person

last slate
# quiet grove yeah

okay so can you please explain to me after this step why we get to that specific formula to calculate all these possibilities?

quiet grove
#

if u want all of them to get at least 1 coin the formula would instead be (n-1)C(r-1)

pearl mist
quiet grove
#

its basically the number of ways of arranging n objects and r-1 partitions

#

imagine u have n objects lying on the ground

#

if you want to make r groups out of them, you have to place r-1 partitions between them

last slate
#

we just give the money

#

in different possible ways

quiet grove
#

do u want a beggar specific derivation 😭

wise flicker
pearl mist
last slate
noble lance
#

do you understand how the beggers and coins correspond to the "objects" and "varieties" from the question

last slate
wise flicker
last slate
quiet grove
#

we love beggars

last slate
#

and the objects is the beggars

wise flicker
pearl mist
last slate
noble lance
#

the correspondence has to make sense to you first, otherwise understanding the beggar variation will not make the original any clearer

last slate
#

like the cupcake one

#

you have 4 varieties and you wanna give to 12 people

quiet grove
# last slate but why

because if you draw 2 lines, it separates the space into 3 parts

so we're drawing 4 lines, which would divide the space into 5 parts, and you put a beggar in each part

last slate
#

so you wanna count the ways that all 12 peoples would get cupcakes

wise flicker
noble lance
#

okay, just quickly, I saw stars and bars mentioned earlier, do you know what that is or have you never seen it before?

quiet grove
last slate
last slate
noble lance
#

okay, that's good, are you comfortable running with stars and bars? that's the quintessential example for this

noble lance
#

suppose that ends up looking something like ★ ★ ★ ★ | ★ | ★ ★

#

with me so far?

last slate
noble lance
#

okay great

#

in this case (★ ★ ★ ★ | ★ | ★ ★) there's clearly 7 stars (objects) and 2 bars (separating 3 varieties)

last slate
#

yea

noble lance
#

that particular example has a mix of all 3 varieties, but you could shift around the bars to show anything right

#

like (★ ★ ★ ★ ★ ★ ★ | |) would mean all stars are of the first variety

#

or you could do (| ★ ★ ★ ★ ★ ★ ★ |) for all stars being of the second variety

#

or really anything

#

in a sense, and this is the key part, all ways to arrange these stars and bars correspond with all the ways you could pick out objects from the different varieties

last slate
noble lance
#

bingo

#

so now our job is a different problem, but if we can do this then we can solve the original problem

#

how many ways can we arrange the stars and bars?

last slate
last slate
#

but thats correct tho right

noble lance
#

well, it's really just stars and bars we're looking at now

#

a particular configuration of stars and bars corresponds with a particular selection of objects of certain varieties

#

in the latter, there's no question of "arrangement" right, it's only about selection

#

but by turning this problem into stars and bars, now it's about arrangement (and no longer about selection)

#

does that make sense? or if not let me know where you got stuck @last slate

last slate
#

im trying to understand the formula

noble lance
#

forget the formula, we're going to build up to that

last slate
#

because that helps me understand what were counting

noble lance
#

does the correspondence of the two problems make sense

#

the key point here is that counting the configurations of one problem is the same as counting the configurations of the other problem

last slate
#

the bars and stars thing

noble lance
#

gotcha

#

let's look at this configuration again: ★ ★ ★ ★ | ★ | ★ ★

last slate
#

okay

noble lance
#

let's just say the objects are balls and the three varieties are red, green, and blue

last slate
#

alright

tribal heron
#

Hmmmm

#

-# beggars/ stars and bars

noble lance
#

this arrangement of stars and bars (where all stars are the same, all bars are the same, it's just the order you care about) corresponds with 4 red balls, 1 green ball, and 2 blue balls

last slate
noble lance
#

in what sense?

last slate
noble lance
#

oh huh okay

#

sure, you could think of the stars as 0s and bars as 1s?

last slate
#

so like what are we doing with tht stars bars/0s and 1s

noble lance
#

right

#

so recall that every configuration of stars and bars corresponds with a selection of objects from the available varieties (and vice versa)

noble lance
#

and we want to count the number of selections

#

so if we count the number of stars and bars arrangements, we will get our answer

tribal heron
#

My sir taught me an excellently simple way of beggars method

noble lance
noble lance
#

yep okay so

#

notice how the stars and bars are just kinda in a line

last slate
#

yea

noble lance
#

in the case above (★ ★ ★ ★ | ★ | ★ ★) there's 7 stars and 2 bars

#

can you recall how many ways there are to arrange 9 objects?

last slate
#

are we doing a permuation

noble lance
#

mhm

noble lance
#

amazing

#

but

#

there's a problem; we have duplicates

quiet grove
#

btw brodie in pnc u have to be able to think of how to apply the formulae creatively to get the harder questions right
so it would help you if you learnt more indirect ways of applying so you get the feel

noble lance
#

consider
★ ★ ★ ★ | ★ | ★ ★
and
★ ★ ★ ★ | ★ | ★ ★
are these permutations of stars and bars the same or different?

last slate
#

like could be a duplicate

#

they are the same tho

noble lance
#

good, and importantly, they correspond to the same selection of objects from varieties

noble lance
#

but actually, I swapped the last two stars and also swapped around the 2 bars

last slate
#

yea

noble lance
#

turns out that didn't make a difference in the end right

#

so we have to account for this

last slate
#

that too

noble lance
#

it turns out that we have to divide by all the permutations of stars, as well as all the permutations of bars

#

so let's quickfire this; we have 7 stars and 2 bars

#

how many ways can we permute 7 objects?

last slate
#

thats 9

#

but I thought we were doing it all together

noble lance
#

nope, we're doing each type of object because indistinguishability is important here

#

when you have a permutation of objects where some are indistinguishable, you have to go through and divide by the permutations of only the indistinguishable groups

#

in this case we have a group of 7 indistinguishable stars, and a group of 2 indistinguishable bars

noble lance
#

with me still? @last slate

last slate
#

im just tryna think of it

last slate
#

what would be wrong with doing permutations on the set of stars and bars together

#

like what would that give

noble lance
#

I'll show you a concrete example that's a bit smaller, so you can see what I'm talking about

last slate
#

okay

noble lance
#

suppose I want the permutations of (1, 2, 3, 3), but the 3s are indistinguishable so swapping them gives me the same permutation

tribal heron
#

-# isn't stars and bars just the distribution of alike things?

last slate
noble lance
#

if I just take a factorial, I will get 4! = 24 permutations, and this is small enough to list out
1 2 3 3
1 2 3 3
1 3 2 3
1 3 3 2
1 3 3 2
1 3 2 3
2 1 3 3
2 1 3 3
2 3 1 3
2 3 3 1
2 3 3 1
2 3 1 3
3 1 2 3
3 1 3 2
3 2 1 3
3 2 3 1
3 3 1 2
3 3 2 1
3 1 2 3
3 1 3 2
3 2 1 3
3 2 3 1
3 3 1 2
3 3 2 1

#

if you look through this list, you will notice duplicates that I did not intend to count

noble lance
#

in fact, I have counted exactly double because swapping the 3s gives me exactly 1 extra copy per permutation

#

so how do I account for this?

last slate
#

which maps to a single set

#

for each duplicate

noble lance
#

what's r here?

last slate
noble lance
#

ah yep okay that's right

last slate
#

wait

#

its 4!

noble lance
#

which, to be clear, is the number of permutations of the indistinguishable objects

#

does that make sense?

noble lance
# last slate its 4!

well, if I divide 4! by 4! I end up with 1 permutation overall which doesn't seem right

last slate
#

Whats the number of permutations here

noble lance
#

I kind of want to ask you that, cuz I'm not super sure where r came from-

last slate
#

were doing 4 permutations

noble lance
#

mhm

#

so we have 4 objects to permute

#

we did 4!, and that gave us 24 permutations

noble lance
#

i.e. we are over-counting, and we need to account for this

#

what should our strategy for that be here

last slate
#

where k is some value

noble lance
#

mhm, and how do we find that value

last slate
#

I thought i knew

noble lance
#

hahahah

#

well

#

notice how if I take one of the permutations

#

say 3 1 3 2

#

and I swap the two 3s, I end up with the permutation 3 1 3 2

#

which, since those are indistinguishable, is actually the same permutation

noble lance
#

right

#

suppose a different scenario where I was instead permuting 1 2 2 2

#

any permution that keeps the 1 there and moves around the 2s will also be the same permutation

noble lance
noble lance
#

in this case, any permutation of the 3s leads to the same overall permutaion, and I have 2 of them, I have to divide by 2!

#

so the answer for permutations of (1, 2, 3, 3) in the end is 4!/2! = 12
1 2 3 3
1 3 2 3
1 3 3 2
2 1 3 3
2 3 1 3
2 3 3 1
3 1 2 3
3 1 3 2
3 2 1 3
3 2 3 1
3 3 1 2
3 3 2 1

#

does this make sense? if not please tell me, because this is crucial before going back to stars and bars

last slate
#

so ⇒ / by variety1! * variety2! * variety3!

#

?

noble lance
#

exactly!

last slate
#

because this is what i was thinking

noble lance
#

yeah I think this is something different, I'm not really sure what the working out there means

last slate
#

for counting subsets

noble lance
#

oh right okay yeah counting subsets is a different problem

#

okay did everything above make sense? shall we go back to stars and bars

noble lance
#

let's go back to this example: ★ ★ ★ ★ | ★ | ★ ★

#

we have 9 objects: 7 stars, and 2 bars

#

how many ways to arrange them?

last slate
#

9!

quiet grove
#

sorry to wander off topic but is the discord.py server from your tag a public server? i cant find it on the explore page

quiet grove
noble lance
quiet grove
#

maybe it has an 18+ filter? i dont see a go to server button

noble lance
# last slate 9!

yep, so as @quiet grove mentioned, we know that there are some indistinguishable objects here, so we have to divide by the permutations within each variety - what do you get when you do this?

noble lance
last slate
#

Hope i didnt cook myself there

#

= 9!/7! * 9!/3!

#

@noble lance

noble lance
last slate
#

Probably wrong

last slate
noble lance
#

hahahah

last slate
#

3 hours of sleep side effects

noble lance
#

I mean you're on the right track but I think you've fallen back onto some old miscalculation habits

#

you shouldn't be doing math on low sleep anyway

noble lance
#

when you're looking for permutations of objects with indistinguishable varieties

#

you do (total number)! / (variety1! * variety2! * ...)

#

that's where we got to yeah?

#

@last slate

last slate
noble lance
#

right, so let's just focus on what the numbers should be to plug into this expression

#

we have ★ ★ ★ ★ | ★ | ★ ★

#

what's the total number of objects here?

noble lance
#

great, so (9)! / (variety1! * variety2! * ...)

#

how many varieties of objects are there here?

last slate
#

wait

#

4 1 and 2

noble lance
#

(what is this thing called again)

scenic star
quiet grove
last slate
#

Sorry bro can we backup a little

#

theres something i need to understand

quiet grove
#

which part

last slate
#

so we need to see how many ways we can rearrange these

#

right

#

without duplicates

quiet grove
#

yeah

noble lance
#

mhm

last slate
#

okay so we know we can arrange them 9! Times

quiet grove
#

and then?

last slate
#

now im tryna understand the duplication part

#

Of why it happens then why does dividing that way gets rid of it

noble lance
#

remember the (1, 2, 3, 3) example?

last slate
#

Yes

#

so is it like

#

in each unique position the 1s can be duplicated 7 times

#

I mean 0s

#

and every unique position for the 1s we have 2! Extra copies of that

#

and we dont want those

quiet grove
#

right

last slate
#

so /7!*2!

#

right

noble lance
#

yep

quiet grove
#

correct

last slate
#

so the whole thing becomes 9!/2!*7!?

quiet grove
#

exactly

#

W

last slate
#

Yesssisisisisi

noble lance
#

🔥

last slate
#

but wait

#

is this how you always do it

#

and like what about the multi set thing

#

or is that counted for

quiet grove
#

what multiset are you referring to

noble lance
last slate
#

like in general i guess

last slate
noble lance
#

i mean all these examples are equivalent right

#

so yeah you can generalize this reasoning in a way

#

okay so we ended up with 9! / (2! * 7!) in the end right

#

but we have to work this back to the first problem, and then it will finally all come together

#

we got 9 as the total number of objects, 2 as the number of bars and 7 as the number of stars yeah?

#

so in general, we can write something like (stars + bars)! / (stars! * bars!)

#

makes sense? @last slate

last slate
last slate
#

i see what’s happening

#

and then we get all slots for how we can get all possible unique arrangements corresponding to each star or 0

noble lance
#

yep

#

so now if we recall how the stars and bars correspond to the original question

noble lance
last slate
#

btw

#

how does this also apply to the math problem

#

like the x1+ x2 +x3 +x4 +x5 = 20

#

for example

noble lance
last slate
noble lance
noble lance
last slate
#

im asking how to apply the stars and bars thing on it

noble lance
last slate
#

its a different problem

noble lance
#

well

#

try to think about what a "star" represents here and what a "bar" represents here

last slate
#

bars or 1s represent seperators

quiet grove
# last slate

first you need to understand why we can use stars and bars, so try to think of what "undistinguishable object" are we distributing

last slate
quiet grove
#

whats your country's currency?

last slate
quiet grove
#

okay

#

so imagine 30 as 30 dollars

last slate
#

Okay

quiet grove
#

you can write 30 dollars as 30 1 dollar notes/coins

#

correct?

last slate
quiet grove
#

would you know the difference between 2 coins?

quiet grove
#

right

#

so the coins here are the indistinguishable object that we are trying to divide into 5 people

#

so basically x1+x2+x3+x4+x5=30 is dividing 30 indistinguishable coins between 5 people

#

so if you use the stars and bars formula that @noble lance helped you understand, you would get the right answer

#

did you get it?

last slate
#

and im tryna see how many ways i can make 30

quiet grove
#

yeah

#

by giving the 5 varieties different amounts

#

exactly

#

so you got it?

last slate
#

thats 30 slots

last slate
quiet grove
#

wdym

quiet grove
last slate
#

@quiet grove @noble lance i appreciate you guys

midnight plankBOT
#

@last slate Has your question been resolved?

midnight plankBOT
#
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last slate
#

update

midnight plankBOT
last slate
#

need help on this one

#

the want at least one kind of each variety in every combination

midnight plankBOT
#

@last slate Has your question been resolved?

last slate
#

<@&286206848099549185>

#

yoooo

hybrid crane
#

You can initially pick 7, all of different varieties. The order doesn't matter so there's only one way to choose that 7.

That leaves 5 donuts to pick, still from 7 choices (with replacement of course)

lilac solstice
lilac solstice
last slate
#

btw im doing bars and stars method

last slate
hybrid crane
#

Then we are left with 5 more donuts to pick

#

That's where you would use stars and bars

last slate
#

same to stars and bars but 0s are strs

#

1 are bars

#

how do i do that now

last slate
#

🤔

hybrid crane
# last slate 🤔

In my mind, you would only forget the first 7 (it'll just add a factor of 1 to your answer). We want to choose 5 items from 7 with repetition/replacement.

As for the layout, there will always be 5 bars and 6 stars - so you can figure it out from there

Had to refresh on stars and bars sors

I think you could do it in full but it'd end up the being the same computation anyway

lilac solstice
hybrid crane
#

At picking 5 from 7, yes

#

(With the aforementioned considerations)

coarse wing
last slate
#

i dont get it at all

last slate
#

thank u

#

but im still struggling with restrictions

#

<@&286206848099549185>

#

Can someone help me understand the restrictions im still confused

#

i mean why are we shortening the set

midnight plankBOT
#

@last slate Has your question been resolved?

last slate
#

<@&286206848099549185> yall recommended i just use this table?

latent wadi
midnight plankBOT
#

@last slate Has your question been resolved?

sudden bronze
#

yo can yall pray for me i got 3 exams tmmr i pray the owner of doge but better does well in his exams

midnight plankBOT
#
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midnight plankBOT
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Available help channel!

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Remember:
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Do not immediately ping people or roles. After 15 minutes, feel free to ping <@&286206848099549185> once.
• Type the command .close to free the channel when you're done.
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Read #❓how-to-get-help for further information on how to ask a good question, and about conduct in the question channels.

vale charm
#

question 2

midnight plankBOT
wooden badger
vale charm
#

its abit messy

#

so i did it to try solve quesiton 2

#

<@&286206848099549185> sorrry kinda tight of time🥲

wooden badger
#

Uhh

#

Theres a triangle

vale charm
#

?

#

for question 2?

wooden badger
#

You can find the angle B using angle sum property

vale charm
#

oooooh

#

THANKSKSS

wooden badger
#

Yassss

vale charm
#

.close

midnight plankBOT
#
Channel closed

Closed by @vale charm

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#
Available help channel!

Send your question here to claim the channel.

Remember:
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vast summit
#

Can someone please check my problem in #forum ??

midnight plankBOT