#help-49
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dude like

what?
There are 18 slots, choose 4 C(18,4) and then arrange A729 4!
Timezone
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
whats it to you
:pepe_cry
4! * 17?
Is it?
I genuinely hate this
why major in stem then
Bro what do they want from me
or are you doing some sort of other science
its just this particular topic of counting
is this breakdown
nah
im gonna continue majoring in stem
Take a nap
||honestly, I hate this sort of counting too
||
exactly
my brain overloaded
this is universal bruh
Try chemistry
i love math but this tests your limits
shall we back to the donut 🍩 
id rather do physics every hour of my life than this
try physics
nick crosses it
Its an option
I'm not good enough at these problems to do that :c
genuinely i can solve these but im kinda bad at explaining
yeah
f#$^ counting

Ts how pnc is
lowkey i wanna hop on vc for this
Invariance, monovariance,etc are far superior forms of combi
Take him @hallow crane
heres the previous topic
Wdym?
Vc
i hate zybooks sm
Nah i would skip
Last night
i told him to do the bars and stars
i mean this probably the simple approach for me i think
$\binom{8 + 3 - 1}{3 - 1} = \binom{10}{2} = \frac{10 \times 9}{2 \times 1} = \mathbf{45}$
linh
Hmm.. usually we jus divide by no. of repeated
read the chatt5

aight
cya
@leon you there
yes
i dint understand what you did there

there are 4 letters that must exist in the mix,
just calculate how much you can rearrange them
let me turn this channel notification off
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)
whats C (18,4)
Combinations
To choose 4 spots
Understand this?
no
When you multiply C (18,4) * 4!
differential equations is easier than this
You get P(18,4)
ye?
@last slate do you truly understand how permutations and combinations works and its theory.
Lmao
i get how premutations work for sure, combination is just permutation but you map r! to a single subset for the duplicated ones
because if you dont get it you cant understand what we are explaining
im not even tryna be funny it actually is
Whose video you sent em?
Leon
You got answer
no
my professor doesnt explain well
ive been self studying my entire career
Except for one class where the professor gave a shit and had some conscience
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 ...
luckily i saved this in my playlist
Crazy was gonna shareda same
@last slate this video probably helps you in self studying
alright thanks, ill check tbis one out
But like
can i still get an explination for that question
th
This
what does P(18,4) do
check the video first
eventually you will found out the explanation by yourself
okay i watched it
but
i already know what it means to do a permutation and combination
but my question was why do a permutation like that one in the first place
why
im saying why
cooked
<@&286206848099549185>
are you asking why you need to do a permutation here
this is your original problem right
whats the set of 18
yes
specifically P(18,4)
why are we considering the lenght
im pasting the problem again for my reference
each valid password
will have to be 18 characters long
now, the restriction states that it must contain a, 7, 2, and 9
yes
now let us look at what the first character of our password can be
it can be any of the 4 characters
yea
we must
then the second characrter can be any fo the 3
because we cannot repeat characters
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
yeah here youre talkin about arranging them in a slot of 4
?
i mean 4 slots
yes of the 18 slots we want four to be the MUST CONTAIN characters
rather
the first character can go in any of the 18 slots
second can go in any of the 17 slots
third can go in any fo the 16 slots
last can go in any fo the 15 slots
now these four characters can be arranged among themsleves in 4! ways
And those 4! Ways can be in different ways in the 18 slots
is that what youre saying
yes
okay i agree
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)!
You lost me here
the first character suppose 'a' can go into any fo the 18 places
the second character '2' can go in any of the 17 places
because a took up one place
accordingly, the third character '7' can go in any of the 16 places
now, the fourth character '9' can go in any fo the 15 places
the answer is for why it's 18 p 4 is understanding it like 18 times 17 times 16 times15
first goes into 18 slots
second 17 slots
third 16 slots
fourth 15 slots
which means 18 times 17 times 16 times 15
Yes but how does the permutation look like for that
okay so
a permutation is
npr which is n! upon r!
here n = 18
and r = 4
so 18! upon (18-4)! would be
18! upon 14!
which is actually just 18 times 17 times 16 times 15
but youre doing the premutation on the 18
which is like what an empty set?
or what
like
what are you putting in slots of 4
we are putting the four characters in 18 slots then 17 slots then 16 slots then 15 slots
so we have picked
4 slots
do you get that
p(n, r) calculates the number of unique arrangements possible when choosing r items from a set of n items
you’re doing a permutation from the set of 18
yes 18 what
what 18 items are we taking
18 places
18 different places where can put the characters in
out of which we just want to put the characters into 4 palces
sure okay
and then in each place the letters can be arranged 4! Times
So thats 4! * P(18, 4) no?
nevermind it aleady counts for it
ue
yup
ye
think of it less in terms of the rigid formula npr
cool
im back
was i able to explain properly
yeah thanks
now time for subsets 😈😈😈
not quite
type .close
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anyone know how to do qn23 b and c?
how would u find the distance between A and B?
that would be the magnitude of AB
which is 20.6
how do u express that mathematically?
the formula for line segment
yeah I've gotten 8.246
Section formula
but how would I find two unknowns x and y coordinates?
You've been given the ratio of AB and AC
but isnt that to find the length segment
not the coordinates?
So you could assume the coordinates as variables and apply tht
Thts distance fornula
Found on Google from geeksforgeeks.org
oh then idk whats section formula
Ts section formula
...?
They asked section formula
Oh
@fossil wagon Has your question been resolved?
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I need some help
what is it asking?
its asking you to use the given mean and standard deviation to calculate exam scores
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
does that make sense
uni
where mu is the mean and sigma is the standard deviation
is it ok to use x bar?
If a score is one standard deviation above the mean, you add one standard deviation to the mean
sure but it doesnt really matter
you dont need to necessarily use variables to answer this question
If a score is two standard deviations below the mean, you subtract 2 standard deviations from the mean
ohhh ok I think i get it now
basically
a higher z score means
more area on the curve
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)
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
did u mean P(z>1.5)
because thats what is written in some of my problems
just a var difference, but sure
@severe grail Has your question been resolved?
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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
rak³en
its alr
This is very similar to that AMC 10/12 problem.
Lmao I have done this one b4 lol
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Oki, so $7 \le d \le 9$
DW
this was my initial approach btw but i saw the options and knew there was some pncier way
Erebus
arent you like excluding zero here
That seems to be the case.
getting the same answer considering from 1 to 9
cant you just safely say 10C7 times 6C3
||10C7 * 6C3 - 9C6 * 5C2|| right?
why so
zero would never come to the first position
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||10C7 * 6C3|| is for all possible cases (including 0)
||9C6 * 5C2|| is for cases where 0 comes first (excluding 0)
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why would zero come first
arent the numbers arranged in descending orderr
I mean I'm using complimentary counting.
yeah but the digits are already said to be arranged in descendign order
nah i think 3219876
Ahh oki
Then ||10C7 * 6C3|| is valid
Since 0 can't be first
(misread the question 😅 )
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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)?
yea?
Like just want to be sure the domain doesnt affect the method, or how its applied right
this method
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Ho can i draw it correctly ?
Draw what correctly?
part b lol
you're not the OP
Who I draw A the symmetric of l with respect o and the others
OP's question was clear enough, so i saved him the trouble of having to rewrite the same thing again
Im thinking if he can't draw a right triangle then im smashing my device
chill, let's focus on op
Symmetric should be smth like O is the midpoint of AL? Im asking for clarity since im not familiar with geometry with english
!noans
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.
Ig im right from the drawing someone deleted 
Sorry
bruh 😭
(just google it)
Finding the third side would be extremely difficult but possible
If that was true
Basically making point B the midpoint 🙏
@odd totem Has your question been resolved?
So in this diagram, you can extend LO such that O's the midpoint of AL
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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.
idiot_max
@thorny folio Has your question been resolved?
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
Yes of course, my bad. Sorry I'm very tired and confused.
Thanks.
To prove that the $f$ has convergency order of $3$, shall I just prove that $\alpha=3$ in the following statement?
\begin{flalign*}
\frac{\left|x_{n+1} - p\right|}{\left|x_{n} - p\right|^{\alpha}} = c
\end{flalign*}
I think I have confused myself with Newton method, fixed-point, and the above statement.
idiot_max
Much appreciate it. And any hint how to find the constant $c$ (asymptotic error const) ? and is it legal to assume $p=0$ ?
idiot_max
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
Thank you. Yes, understood.
Thank you so much sir, really really appreciate your time and consideration. Math bless us all.🍻🤓🤘
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Yes
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gggggg LALALAL (supposed to be a really dramatic entrance)
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
Maybe you should send us a photo of it
wdym
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
of their intuition?
It shouldn't be too bad if they already have the intuition for the problem
ouuuuu
Well this is it 
pick a basis
ok how did you show the first part...
<@&268886789983436800>
pick a basis for A + B 
Picked basis for A and B, combined, then showed that the set spans A+B
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
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I am so lost how to do this
Where is c and w?
I mean w
Oh so 1 is suppose to be 1w?
Acc to the formula yes
€C=275x1w+150+25n
Yesyes
Okay so now for 4b uhhh
I think so too
U hv this fornula
Four people=100n?
€C=275x2w+150+100n?
And then I have to work out the value of c?
Yup
Lowkey forgot but I will try
Forgot what its js calculation TT
I need to serpate the w's and the n's on different sides?
For question b they provided the w's and the n's so you just substitute them
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Hi i need help understanding the logic behind this formula
Thte ncr?
what?
its called the stars and bars method u can check it out on yt
i did but they don’t explain it properly
i just need someone to explain to me the intuition
read this once
use it when you want to distribute identical objects in distinct boxes or people
Ooh the gap method
yeah but it finds what
the amount of what
and does it count duplicates
number of ways to distribute identical objects among distinct people
maybe thats why i learnt it as beggars method
yeah
say you had a variety of four flavored cupcakes
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
this wouldnt be applicable here because the cupcakes are distinct
neither are the people so u cant manipulate it in the opposite way
well i suppose you dont distribute people among cupcakes
you need identical cupcakes and different people
is this the whole “distinguishable” vs indistinguishable thing
for God’s sake explain this to me man ive been trying to understand that too
@quiet grove
if 2 things are the same they are undistinguishable
2 people are not the same so they are distinguishable
Stars and bars applies directly only to identical objects
a vanilla and a glaze cupcake are not same so they are distinguishable
look ill tell you this the way i learnt suppose there are 10 beggars well each person is different and you want to give them money say 5 bucks each can you distinguish each set of 5 bucks for all the beggars? no bc money is money but can you distinguish the beggars? yes
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
yeah
You can do this way, how many ways can you cholse flavour for 1 person
yeah and
and what are we counting for
what multisets are we counting here
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
number of ways you can give 1 coin to the beggars
(4+2-1)C(2-1)=5C1=5
and we got 5 cases here as well
okay wait how many beggars do we have as an example?
just as an example like say 5
okay and they are distinguishable
now what
ok so there are 5 beggars and you have to give each one of them one coin so you should atleast have 5 coins ryt
yes
right
so here m and n both are 5; 5 coins and 5 beggars
And we are trying to find what multisets exactly
multisets as in?
like sets with repeated objects
the whole section is titled “counting multisets”
{1,2,2,0,0} {1,1,1,1,1} {1,0,3,1,0}... etc
each slot being a person?
yaah
wait so not all of them get money
and the number is number of coins
yeah
because the formula u sent specifies there are no restrictions on how much can go to each person
okay so can you please explain to me after this step why we get to that specific formula to calculate all these possibilities?
if u want all of them to get at least 1 coin the formula would instead be (n-1)C(r-1)
not necessarily the formula still works if you have 5 beggars and 4 coins whatever may be the number of ways one beggar will not get a coin
i sent u a pic with the explanation read that first nd lmk if u get it
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
but there isnt any paritions when i rearranging the money to the beggars
we just give the money
in different possible ways
do u want a beggar specific derivation 😭
Lmao beggars act like slots

not necessarily
do you understand how the beggers and coins correspond to the "objects" and "varieties" from the question
okay yeah but there are no seperations
There's a reason ts famous as beggar's method
i guess so the money is the variety
we love beggars
and the objects is the beggars
Put no. of beggars-1 separations
ts looks ugly
but why
I think it's the other way around? because each beggar can get multiple coins
and in the question, each variety can yield multiple objects
the correspondence has to make sense to you first, otherwise understanding the beggar variation will not make the original any clearer
i don’t understand bro can we do a different analogy where the numbers arent the same
like the cupcake one
you have 4 varieties and you wanna give to 12 people
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
so you wanna count the ways that all 12 peoples would get cupcakes
okay, just quickly, I saw stars and bars mentioned earlier, do you know what that is or have you never seen it before?
if you want ALL the people to get at least 1, theres a separate formula for that
ive seen it but its very confusing
i see, can we please start with were its allowed for one of them to not get a cupcake
okay, that's good, are you comfortable running with stars and bars? that's the quintessential example for this
let's say our n objects are stars. we have all of them in a line, but each may come from a different variety. let's group them into the m possible varieties, and separate each group by a bar.
suppose that ends up looking something like ★ ★ ★ ★ | ★ | ★ ★
with me so far?
maybe
yes
okay great
in this case (★ ★ ★ ★ | ★ | ★ ★) there's clearly 7 stars (objects) and 2 bars (separating 3 varieties)
yea
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
so the point is you count how many ways you could have 7 of 3 varieties?
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?
And are there duplicates
ngl i cant seem to think of it like that, i can only see it as “how many ways can you arrange m varieties to make up n “
but thats correct tho right
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
ngl its not
im trying to understand the formula
forget the formula, we're going to build up to that
because that helps me understand what were counting
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
its not really clicking for me
the bars and stars thing
okay
let's just say the objects are balls and the three varieties are red, green, and blue
alright
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
wait is this the same as mapping to a string of bits?
in what sense?
yes i get it now
so like what are we doing with tht stars bars/0s and 1s
right
so recall that every configuration of stars and bars corresponds with a selection of objects from the available varieties (and vice versa)
yea
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
My sir taught me an excellently simple way of beggars method
so the question is this: how many ways can we arrange the stars and bars?
yeah how do you know
yea
in the case above (★ ★ ★ ★ | ★ | ★ ★) there's 7 stars and 2 bars
can you recall how many ways there are to arrange 9 objects?
are we doing a permuation
mhm
9!
waya
ways
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
consider
★ ★ ★ ★ | ★ | ★ ★
and
★ ★ ★ ★ | ★ | ★ ★
are these permutations of stars and bars the same or different?
could be different
like could be a duplicate
they are the same tho
good, and importantly, they correspond to the same selection of objects from varieties
yea
but actually, I swapped the last two stars and also swapped around the 2 bars
yea
turns out that didn't make a difference in the end right
so we have to account for this
that too
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?
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
(consider if I swapped a star and a bar, then you actually would be able to tell the difference)
with me still? @last slate
wait so
what would be wrong with doing permutations on the set of stars and bars together
like what would that give
I'll show you a concrete example that's a bit smaller, so you can see what I'm talking about
okay
suppose I want the permutations of (1, 2, 3, 3), but the 3s are indistinguishable so swapping them gives me the same permutation
-# isn't stars and bars just the distribution of alike things?
true so how does doing them separate solve that
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
true
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?
you divide by r!
which maps to a single set
for each duplicate
what's r here?
2!
ah yep okay that's right
which, to be clear, is the number of permutations of the indistinguishable objects
does that make sense?
well, if I divide 4! by 4! I end up with 1 permutation overall which doesn't seem right
but r is the number of permutations
Whats the number of permutations here
I kind of want to ask you that, cuz I'm not super sure where r came from-
this is what I want to count
I don’t get it
were doing 4 permutations
but when we list out the permutations, we see that there are duplicates
i.e. we are over-counting, and we need to account for this
what should our strategy for that be here
That was like dividing by k
where k is some value
mhm, and how do we find that value
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
yes
I agree
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
right
because any permutation of 2s leads to the same overall permutation, and I have 3 of them, I have to divide by 3! (since that's how much I'm overcounting by)
yes
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
exactly!
because this is what i was thinking
yeah I think this is something different, I'm not really sure what the working out there means
its a k to 1 mapping
for counting subsets
oh right okay yeah counting subsets is a different problem
okay did everything above make sense? shall we go back to stars and bars
yes
let's go back to this example: ★ ★ ★ ★ | ★ | ★ ★
we have 9 objects: 7 stars, and 2 bars
how many ways to arrange them?
9!
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
remember that 7 stars are alike and 2 bars are alike
yep should be, just click on it no?
maybe it has an 18+ filter? i dont see a go to server button
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?
no idea, the invite is in the library's documentation page - https://discordpy.readthedocs.io/en/latest/
Ok so lemme do it like this
you want how many ways to arrange
000010100
Such that 0s coresponds to different varities and 1s are separaters
So then you wanna know how many ways to rearrange the 0s and 1s so you know that you can arrange the 0s P(9, 7) /7! * P(9,3)/3!
Hope i didnt cook myself there
= 9!/7! * 9!/3!
@noble lance
what happened to this?
Probably wrong
I forgot what i was thinking
hahahah
3 hours of sleep side effects
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
let's go back to this idea, cuz this was spot on
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
yea
yes
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?
9
great, so (9)! / (variety1! * variety2! * ...)
how many varieties of objects are there here?
I literally mean like in ★ ★ ★ ★ | ★ | ★ ★
(what is this thing called again)
7?
Stars and bars?
7 of what
which part
the part where we need to rearrange 000010100 certain times
so we need to see how many ways we can rearrange these
right
without duplicates
yeah
mhm
okay so we know we can arrange them 9! Times
and then?
now im tryna understand the duplication part
Of why it happens then why does dividing that way gets rid of it
remember the (1, 2, 3, 3) example?
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
right
yep
correct
so the whole thing becomes 9!/2!*7!?
Yesssisisisisi
🔥
but wait
is this how you always do it
and like what about the multi set thing
or is that counted for
what multiset are you referring to
for permutations with repeated (indistinguishable) objects, yes
like in general i guess
and that works for the cupcake example
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
My bad phone died
yea
yes
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
if we go back to this message, we could work out that stars = n and bars = m - 1, yeah?
yes
btw
how does this also apply to the math problem
like the x1+ x2 +x3 +x4 +x5 = 20
for example
sorry what do you mean by this?
plugging this in, we get that the number of ways to select n objects of m varieties is (n + m - 1)! / (n! * (m - 1)!)
um, this is a different problem?
same concept tho no?
im asking how to apply the stars and bars thing on it
I'm looking at this problem you sent earlier
ah sure okay
well
try to think about what a "star" represents here and what a "bar" represents here
Stars or 0s represent positions
bars or 1s represent seperators
first you need to understand why we can use stars and bars, so try to think of what "undistinguishable object" are we distributing
i don’t understand what they are tbh
whats your country's currency?
dollars
Okay
yes
would you know the difference between 2 coins?
no
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?
so i have 5 varieties
and im tryna see how many ways i can make 30
thats 30 slots
id need to know my solutions tho?
wdym
5 slots 30 coins
lenme get some rest and get back to it 🤣
@quiet grove @noble lance i appreciate you guys
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update
need help on this one
the want at least one kind of each variety in every combination
@last slate Has your question been resolved?
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)
List out the combinations.
Then do calculations.
I don’t understand the part about havin at least 1 selection
btw im doing bars and stars method
@lilac solstice
Since the order doesn't matter, I could fulfill the requirement of having 1 of each kind by just picking 7 donuts of different variety
Then we are left with 5 more donuts to pick
That's where you would use stars and bars
so the thing is im trying to think of this via rearranging like 111111000000000000
same to stars and bars but 0s are strs
1 are bars
how do i do that now
what’s gonna be different in my rearranging tho i dont get it
🤔
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
Actually I would just list down the possible combinations (not all but the available spaces as empty lines) then calculate.
so youre looking at 5 donuts?
i dont get it at all
oh yeah thank God
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
@last slate Has your question been resolved?
<@&286206848099549185> yall recommended i just use this table?
Yes but i recommend that you should understand where these formulae come from
@last slate Has your question been resolved?
yo can yall pray for me i got 3 exams tmmr i pray the owner of doge but better does well in his exams
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question 2
What hv u done?
its abit messy
so i did it to try solve quesiton 2
<@&286206848099549185> sorrry kinda tight of time🥲
Yassss
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Can someone please check my problem in #forum ??





