#help-28
1 messages · Page 153 of 1
once you have all the cases of 2 tails you can just mirror it to get the cases of 2 heads
in total, yes, 8
because you have 2 possiblities for each of the 3 trials
so 2 * 2 * 2=8
yep :)
So basically
2³ = 8
2 - heads or tails of a coin
³ - cuz of the toss counts
6 - the total number of heads or tails combined?
6 comes from the number of cases out of the 3 coin flip trials that have 2 tails or 2 heads
So in simple terms, 6 comes from the possibility of getting heads or tails in the 3 coin flip trials?
6 represents the total possible ways to get 2 heads when flipping a coin 3 times + the total possible ways to get 2 tails when flipping a coin 3 times
that's 3+3=6
Ohhhhhhhh
So is this correct? Except for 6?
@velvet sedge I still don't get the idea, how about for number 2?
Atleast a tail or 3 heads
So P(1 tail, 3 heads)
think of or as 'adding' the probabilties together if you can't consider them together
$P(A \cup B)=P(A)+P(B)-P(A \cup B)$
MSC2020 55N31 (Moosey)
$P(A \text{ or } B)=P(A)+P(B)-P(A \text{ and } B)$
MSC2020 55N31 (Moosey)
but P(A and B) in this case doesn't make sense, because you can't have 3 heads and 1 tail in 3 coin flips
so we say its 0
So P(0, 0)?
no...
let A=atleast 1 tail in 3 coin flips and B=3 heads in 3 coin flips
whats the P(A)
whats the P(B)
no..
P(event)=(how many ways out of the 8 total ways does this event occur)/8
so out of the 8 total possiblities of flipping a coin 3 times, how many of those have 3 heads
1 right?
Yeah
Idk
it's also easier to think of this as 1-P(not A)
what's the opposite of atleast 1 tail
Atleast 1 heads?
no...
atleast 1 tail means there is always atleast 1 tail, there's always a tail.
what is the opposite of having a tail in your 3 coin flips
Getting all heads.???
yes!
But why???
well think about what atleast 1 tail means
THH has atleast 1 tails, TTT has atleast 1 tail
Ohhhhhh
I see
Where did u get 7?
1-1/8
or you can think about just getting rid of the HHH case out of the 8 total cases
Oh so basically
P( atleast 1 tail) = 7/8
P(3 heads) = 1/8?
7/8 + 1/8 = 8/8
= 1
@velvet sedge
yes
or you can think about it more simply like P(atleast 1 tail)=1-P(3 heads)
then 1-P(3 heads)+P(3 heads)=1
The reason why P(B) = 1/8 is because you can only get 1 HHH out of the coin flips?
yes
well this one you HAVE to account for P(A and B)
Why is that?
P(A or B)=P(A)+P(B)-P(A and B)
because both can occur at the same time
you can have a head and 2 tails
Is P(B) = 2/8 correct?
what is B? the probability of having 2 tails in 3 coin flips?
Yeahh
yes
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Well what's one of of computing it?
wdym?
holy shit I was so confused, like "why is that thing raised to the fourth power"
yeah that confused me too
now I see it's just a reference to somewhere else
Well
<v, Av> = ..?
What can you simplify here
<A*v, v>
Yes that's one way
= <-Av, v>
what now
-Av = ?
hm
0??
Yes
so we get <-lambda * v, v>?
= (-lambda)* <v, v>
so lambda<v, v> = (-lambda)* <v, v>
which part?
$\inner{v}{Av} = \inner{v}{\lambda v} \neq \lambda\inner{v}{v}$
RedstonePlayz09
At least not over C
i think my lecturer defined it in the opposite way
That's weird why would they define it this way lmao
Yeah ok sure
$$\inner{v}{Av} = \inner{v}{\lambda v} = \lambda\inner{v}{v}$$
\medskip
And also:
\medskip
$$\inner{v}{Av} = \inner{A^*v}{v} = \inner{-Av}{v} = \inner{-\lambda v}{v} = \conj{-\lambda}\inner{v}{v} = -\conj{\lambda}\inner{v}{v}$$
RedstonePlayz09
this part makes sense i think
yeah
So you got anymore questions?
@raw girder Has your question been resolved?
nope, thanks for ur help 🙏
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give an example
rectangles
90degrees
what is the question here?
here, every intersection is perpendicular
theer are 3 right angles in every corner
in 3 different faces of the cuboid
@torn jolt Has your question been resolved?
what is the actual question in the book?(or the source)
make a grid of the 3d shape
like what you get by cutting open a paper cube box
then combine the results
deal with 1 face at one time
like?
you would need to use trigonometry
think of the faces as rectangles, so the corner has a right angle
even if you rotate along the edge, the angle will remain the same, as long as the adjacent edges are moved
@torn jolt Has your question been resolved?
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hey can anyone help me with this
for the first one i did 22190/2 so 11,095 is the expected number of males
for the second one i did 2-1 so 1 degree of freedom
hi
hey
whats your prob?
i posted the picture
ok
would it be 0.05>p>0.01?
i think its.
ye prob
.close
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If I have a ratio of 1:74, and the numerator is 17,952, what will the denominator be?
I believe you start by setting up a proportion 1/74 = 17952/x and solve for x
I don't think they allow giving the answers directly ill check the rules
Oh for real? its fine mb
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Is the answear for i) wrong or hiw is it 0?
It's definitely not 0
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did i get these right?
Please don't occupy multiple help channels.
@warm cargo Has your question been resolved?
@warm cargo Has your question been resolved?
<@&286206848099549185>
@warm cargo Has your question been resolved?
I agree with your answers for 1 and 4, but for 2, you should check the roots of that again. If you plug x=8 back in, it doesn't work out
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oh srry uh
i actually dont even know how to set up the equation
😭
<@&286206848099549185>
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circle b and circle c is 1/8 of original circle
so combined 1/4
the overall area of the triangle is 18
@craggy tapir
are you gonna help me?
im looking at the problem
can you calculate the radius of the big circle?
hint: draw AH perpendicular to BC
the radius will be AH
a point you construct it yourself
@meager garnet Has your question been resolved?
alright, the radii are easy to find, are you done calculating that?
angle B and angle C is 45 degrees
area of a sector of a circle is given by $\frac{\theta}{2}r^2$
zelphanine
where r is the radius
find the areas of all the sectors
then find the area of the full triangle
the difference should give you your answer
@meager garnet
can you confirm that this is the radius of circle A?
@graceful yoke
no it will be sqrt(3)
draw a line from point A to the midpoint of BC
call the new point D
triangle ADC will be a right angled isoceles triangle
apply pythogoreas theorem on it
ah sorry my bad i did a calculation mistake
yes it is 3*sqrt(2)
sorry about that i forgot to square the 6 while applying pythagoreas
now to find the radius of the smaller circle, observe that the sum of the radius of the big circle and the radius of the small circle is just 6
yes
i got 1.4379
big circle area is 14.1371
and the two smaller circles make up 2.4255
and the whole triangle is 18
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can someone help me with composite functions
g(f(x) = (4x+1)^3 +1
to find g(f(0) first evaluate the value of f(0)
0 is x right
yeah
f(0) = 4(0)+1 [ replace x with 0]
therefore f(0) = 1
now replace f(0) with 1 in g(f(0) = g(1)
oh so 4x0+1
i didnt get the last part
from which part exactly ?
substitute 1 in place of x of g(x) function
yes so g(1)
where do u get x^3 from
g(x) = x^3+1
then why did we use 4x+1
When you see g.f(0)
You start with the last function listed and work towards the first one
is it bc g is in the first one and f is in ther 2nd one
but what if it was gh(0) then would we use the one that contains h in it like this one
Exacty
OHH
You start with H first because it’s the second one listed
Then when you find the result you use that in g
ok ok so wait the vlaue of g is g(1)
now we go to f
and there it says x^3
so should we replace
that
1
?
For g(f(0))?
ok one sec lemme try to solve it
can we say like since we found f now we will go to g and for g there is x^3 so we replace this with 1 and it would become 1+1=2
can we solve liek thid
Yes that’s correct
ok i will ssolve the 2nd one its
find fg(x) simplfy ur answer
wait i dont know how to solve this
Ok so this time notice you don’t have a value to substitute into g(x)
ya
So instead you replace x in the second function ( which is f(x) ) with the entire function g(x)
so f=x^3+1?
f(x^3+1)
oh
So replace every x in f(x) with (x^3+1)
so 4(x^3+1)+1
Dont forget the +1 at the end
yep i forghet
Yeah that’s right
Yep
Have you learnt to find inverse functions?
h(x)=2x+1/3
kindaa i just know at the last step it must be f^-1 something
and that
we
need
to
rearrange
it
Luca M
You could also, if it makes it easier, let y = h^-1(x)
Then it becomes
$x=2y+\frac{1}{3}$
Luca M
Now solve for y
Your simply swapping x and y, which is the definition of an inverse function
Yeah
Do you know the formula for the volume of a cylinder?
Right. What is the radius in this case?
uhhh
Oh it tells you in the question
Length 11cm is the same as height 11cm
oh
Now all you have to do is substitute those values in and divide your result by 2
pi is 2.14?
3.14159
Notice it is the volume of half a cylinder
pi*r^2h is the volume of a full cylinder
So we must divide by 2 to get the volume of one half
so 3.14x6^2x11
Yes, then divide that by 2
And make sure to write down cm
I got 621.72 cm
Did you enter it right in the calculator
oh ya i got 621.72
Nice
i put something wrong
ok i have a hard question
this
is
thw
lastt
this one
Do you know where to start for a) or b)
nope not rlly..
Do you know formula for volume of the prism
Not in this case
Base and height refer to the cross section of the prism
Which is the right angle triangle
Length is how far in the 3d world the triangle goes for
@cunning radish Has your question been resolved?
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can anyone help me with this, not sure how to do it
ill try
how?
meaning A takes 3 hours to fill it halfway
yep
and B takes 2 hours
so
turn on A for an hour
then B
then A
Then B
then A
the 2 hours
B was on
it filled up halfway
and
the 3 hours
A was on
it filled up half way
now the tank if full
its all about thinking how much can they fill up in an hour
i couldnt do that
so i just thought
how many hours to fill it halfway
do you get it?
can you explain from the halfway thing
yes
why half it though?
because we want to shorten the time interval
to calculate more precisely
oh ok
the same applie to pipe B
half the time
half the tank
so 2 hours fill up half way
now we just
play it our
turn on pipe A
for an hour
then pipe B
then pipe A
then pipe B
then pipe A
the 2 hours B was on
it filled up halfway
and the 3 hours A was on it filled up halfway
how do we know how many times they have to be turned on and off till the tank is full
the options
try the options
A option
is 4 hours
and i can see on hour 4
its imposible for the tank to be full
so naturally i turn it back on for more time
ok
and when i tried 5
i saw it fit perfectly
1st hour: Pipe A fills 2/12.
2nd hour: Pipe B fills 3/12 of remaining 10/12.
3rd hour: Pipe A fills 2/12 of remaining 7/12.
4th hour: Pipe B fills 3/12 of remaining 5/12.
5th hour: Pipe A fills 2/12 of remaining 2/12.
6th hour: Pipe B fills the remaining 2/12.
So, the tank shall be full after 6 hours.
that ain't even in the options
probably can but i cant think of it
its ok
like i solve using more logic
1st hour: Pipe A fills 2/12.
2nd hour: Pipe B fills 3/12 of remaining 10/12.
3rd hour: Pipe A fills 2/12 of remaining 7/12.
4th hour: Pipe B fills 3/12 of remaining 5/12.
5th hour: Pipe A fills 2/12 of remaining 2/12.
If we add up the fractions filled by each pipe, we get:
2/12 + 3/12 + 2/12 + 3/12 + 2/12 = 12/12
yep sorry ans is 5h
i think this is algebra
2+3+2+3+2 is what?
1st hour: Pipe A fills 2/12.
2nd hour: Pipe B fills 3/12 of remaining 10/12.
3rd hour: Pipe A fills 2/12 of remaining 7/12.
4th hour: Pipe B fills 3/12 of remaining 5/12.
5th hour: Pipe A fills 2/12 of remaining 2/12.
Starting with Pipe A: Since pipe A is opened first, it fills the tank for the first hour.
Second Hour with Pipe B: Then, pipe B fills the tank for the second hour.
Alternating Hours: This pattern continues, with pipe A filling the tank during odd-numbered hours and pipe B filling it during even-numbered hours.
Now, let's see how much of the tank each pipe fills in one hour:
Pipe A fills 1/6 of the tank in one hour (because it takes 6 hours to fill the tank completely).
Pipe B fills 1/4 of the tank in one hour (because it takes 4 hours to fill the tank completely).
Now, if we alternate between these pipes every hour, we can calculate the total time it takes to fill the tank.
1st hour: Pipe A fills 1/6 of the tank.
2nd hour: Pipe B fills 1/4 of the tank.
3rd hour: Pipe A fills another 1/6 of the remaining tank.
4th hour: Pipe B fills another 1/4 of the remaining tank.
5th hour: Pipe A fills the remaining 1/6 of the tank.
Adding up these hours, we see that it takes 5 hours in total to fill the tank.
So, the tank shall be full after 5 hours.
did u get it now?
yep thanks a lot bro
do you want us to close this
i am gona close it
so others can use i
it
.close
whoever started this
close it
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Yes
now We want to find the number of sequences of rolls where the largest number appearing is not 4
consider cases where the largest number is not 4
so the largest number appearing can be 1,2,3,5 or 6
for each throw
there are 5 possible outcomes to meet that solution
or condition
Yes
Mhm
how do you write that as a number
There's a catch
what
Suppose I took the dice 4 times and I get 1,1,2,2
I do it again, I get 1,2,1,2
In the list they will be treated the same
But 5^4 counts it 6 times to be precise
Similarly 1112, 1211,1121,2111
Same thing with 4 ways
ok then the lowest one
The number of time each case gets repeated
Can't divide by just 1 number
It's complicated ig
Like aaaa will occur once time
aaab will occur 4 times
aabb 6 times
aabc 12 times
abcd 24 times
I hope I'm making sense
Ig
yeah i know what you are saying
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Bit stuck with this
multiply the two things
use vieta's relations to evaluate the extra terms that come up
I was just wondering if there was a faster way
but Ill do that now
I just have a big expression and I can't really see how to apply it
@white delta Has your question been resolved?
<@&286206848099549185>
@white delta Has your question been resolved?
faster way, see:
https://artofproblemsolving.com/wiki/index.php/Newton's_Sums
yeah never seen this before, I was jsut doing papers from other schools and thought I'd learnt what i'd needed to do it
thanks though
.close
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A train arrives at a station 3 times an hour. It stops 2 minutes each time.
What are the chances Helena has to wait 10 minutes or less?
This is the question but I'm struggling to understand the explanation for how to solve it.
"In one hour, there are 60 minutes, and the train stops three times per hour.
If the train is already at the station, she can board it directly. Since the train stops for two minutes each time, it spends a total of 3⋅2=6 minutes at the station in one hour.
She needs to wait less than ten minutes if she arrives 10 minutes or less before the train arrives. Therefore, we can add 3⋅10=30 minutes to the 6 minutes the train spends at the station 36/60 = 60%"
I don't really understand the adding 30 minutes part?
@winged fog Has your question been resolved?
imagine you have all 60 minutes of the hour and you call them either a good minute if you have to wait less than 10 minutes for the train, a neutral minute if the train is already there or a bad minute otherwise
then there are 30 good minutes, 6 neutral minutes and 24 bad minutes
so 36 minutes out of 60 are what you want
(this is assuming that the train leaves regularly and not something like 3 times within 15 minutes and then never in the remaining 45 minutes)
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The matrix $A_{8\times 6}$ has 6 linearly independent column vectors from R^8.\
Can one claim that any of the matrices Are $A^T * A$ and $AA^T$ surely invertible, or, alternatively, singular (ie, lacking an inverse)?
Hint: $B^{−1}$ does not exist if $Bx = 0$ for some x ̸= 0. In that case x is also $x^T Bx = 0$. Interpret then $B = AT A or AAT$
use \times
where
8 \times 6
🤷🏼 w/e
The matrix $A_{8\times 6}$ has 6 linearly independent column vectors from $R^8$. Can one claim that any of the matrices Are $A^T * A$ and $AA^T$ surely invertible, or, alternatively, singular (ie, lacking an inverse)?
Hint: $B^{−1}$ does not exist if $Bx = 0$ for some $x\neq0$. In that case x is also $x^T Bx = 0$. Interpret then $B = AT A $or $AAT$
FungusDesu MSC2020 34A05
Compile Error! Click the
reaction for more information.
(You may edit your message to recompile.)
eh good enough
for helpers, this is the question
For the $A^T A$ case, try showing $A$ and $A^T A$ have the same kernel
AlphaNull
kernel?
Ideally i'd like to understand the question first
what part do you not understand?
I'm given a matrix which has 6 colon vectors that are R^8? Right?
yes
"Can it be said that $A^T * A and AA^T$ are inversible or are missing invers"
Merineth
What does inversible mean?
Is that essentially the same thing?
Inversible and missing an inverse
no, they are opposites
invertible means there exists some matrix $A^{-1}$ such that $A \cdot A^{-1} = A^{-1} \cdot A = I$
AlphaNull
Okay so it's asking me if the matrix is inversible or missing an inverse?
Is there a specific condition that has to be fulfilled for it to be inversible / missing an inverse? Doesn't it have something to do with determinants ?
If the determinant is not 0 then there exists an inverse?
that is true but you can't use that
have you heard of the invertible matrix theorem?
No
you should probably look it up
it has a lot of equivalent statements for invertibility
by the end of a linear algebra class most of them will seem quite obvious
yeah the hint says use the null space property
We don't have a teacher so kind of hard to learn this myself
if you are using a good book you should be fine
I am not
then use a better one?
I don't know what null space of A being 0 is
why are you doing this question if you havent learnt null space yet?
Because it's an assignment due soon
well i suggest learning null space then
im not allowed to give you answers sorry
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tysm 👍 :)
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i dont understand c
they need to find a formual
the worked example explained it: but idk where the formula came friom
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so is that [-1.5, 1] U [4.5, infinity)?
I can't tell you the precise values with the only info present in this graph
do I have to make it clearer?
No no
It was not the image quality the problem, but the fact that you're not given the expression of those two functions
Not only there
where else?
Where it wasn't here
hm not sure
do you mind showing me where on the graph, I'm still confused a bit
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Wanting to know wether this process is right or wrong
u can take derivative of the final answer , if its equal to the question then its right
It’s wrong
The formula you’re using is only valid when it’s just x
it looks like you made a u-sub error
Not x^{3/2}
Oooh i see
this integral is a terrible one to do by hand
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If I have a non-square m x n matrix whose columns are linearly independent, does that mean if I multiply this matrix by its own transpose, the columns are still linearly independent?
is m<=n?
m>n
umm then it's definitely false right
Yes, mostly
A is of size mxn
A^t is nxm
so A A^t is mxm
the rank of A and hence the rank of AA^t is n (because it has n independent columns)
so there's no way an mxm matrix has all independ. rows but rank only n < m
n is the number of columns so its the number of vectors
if n > m then the columns are def not independent
yup that's also true
so i guess the only case this can work is m=n
in whcih case the answer is indeed yes
otherwise its always no
hm alright
but let's say i multiply A^t A instead of A * A^t then, is it still false?
this time it's nxm * mxn, so the matrix is now nxn if i'm not schizo
sure
no no you can have lin independent vectors if m>n

A can have lin indep. columns if m>n yes. But AA^t cannot
yes in this case the answer is yes
because it's rank will be n
and the matrix is of size nxn
If $A_{6x8}$ then $AA^T a$ results in a 8x8 matrice
Merineth
Merineth
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could someone help with this problem
I have
some work if helpers would like me to send
essentially I plugged in each f(x) into the given formula to set up a system of equation
yes send your work
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X1245 generates $100 in free cash flow every year, but it has a 50% chance of breaking down every year. What is the value of X1245?
How would I go about solving this?
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<@&286206848099549185>
This is a somewhat open ended question and I don’t know if there’s some kind of business algorithm or whatever for it, but I’d say just divide its value by 2 every year and sum the infinite series
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Haven’t taken a math class in a bit, any advice on how to sum an infinite series?
It would be this right?
.50(100+.5(100+.5(100+…)))
Yes
Although you should also have a 1(100) term
To sum a geometric series you take a/(1-r) where a is the starting value ($100) and r is the value you’re compounding exponentially (in this case .5)
When you write it as $100 + $50 + $25 + … you can intuitively get the sum as well (and it nicely corroborates the formula)
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Topic: Calculus, Convergence
I get that from 0<x<2pi sinx will always be between -1 and 1, but
can someone explain the underlined part?
if x is an odd multiple of pi/2 then sin(x)=1 or -1
ooh right cause -1 and 1 are not included omg
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<@&286206848099549185> what does recursive formula means and what do we mean also by closed formula please
!15m
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It already passed 😬😳
@torn jolt Has your question been resolved?
@torn jolt Has your question been resolved?
@torn jolt a recursive formula is a formula that is defined by previous values in the sequence.
For instance the Fibonacci sequence is defined recursively.
F_0 = 0
F_1 = 1
F_n = F_{n-1} + F_{n-2}
A closed form solution to a recursive formula is when you solve the recursion and remove it
For the Fibonacci sequence this is
F_n = ((φ)^n + (-φ)^(-n))/√5
Where φ is the golden ratio: (1 + √5)/2
For linear recurrences it is generally possible to find a closed form solution. There are a handful of techniques. For non-linear ones, though, it's pretty much hopeless.
So for example we have got p(n)=p(n-1)×2+1 with p(1)=1 , that's the recursive formula, when i want to write the closed formula, it will be p(x)=2powern -1 , so what i did here is that i I generalized the expression for the sequence to include all terms ? Is that correct?
Sorry but i am just new to this and it's confusing me😭
You removed the dependence on p(n-1) from p(n)
I don't think "generalized the expression for the sequence to include all terms" is accurate
The sequence already is defined for every positive integer.
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can anyone help me with these probability questions? all help appreciated!!
What question?
can i start with 1B?
I don’t know what the bars above the numbers mean
letters sorry
Are they replaced or not?
replaced?
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For the joint probability 𝑃(𝐶,𝐷, 𝑅, 𝑆) state its factorised form in terms of its constituent conditional probabilities for all events. What does this question mean?
So this is the question:• C for the coin
• D for the dice
• R for the event that coin is heads OR dice is six
• S for the event that coin is heads AND dice is six.
and the answer I got is -> P(C) X P(D) X P(R given C OR D) X P(S given C AND D AND R)
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still wanting the answer?
Yes
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what is that
logarithm
!occupied
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Based on what you have said, I don't see anything wrong with your work. However, it would probably be more useful to everyone if you posted the original question in full context.
Okay
This is the question
And im looking at bi
And i am not sure how to represent R
R | c or d
But how would i write that? As p(R|c,d) or p(R|c or d)
Yes, but I would not consider that to be a fully factorized version
So how can i fully factorise it?
Using the definition of conditional probability
so like the equation on the left side?
Oh so this will need to be expanded more?
I see
Hmm
You should find that a lot of things cancel.
You'll probably need to also use the independent of C and D to break apart P(C and D) and P(C or D) into P(C) P(D) and (P(C) + P(D) - P(C) P(D)) respectively.
I think you have all of the information that you need to tackle this problem. But your textbook should have any relevant formulae if I missed something
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yo
2(5x+21)
can i get help with this
i got this far but idk what to do now that there is x on both sides
take away 9x from both sides
54 = x + 42
then take away 42 from both sides
12 = x
for this one would i make them equal to eachother?
nvm i would
can someone check this i got 12
is the answer 12 @dense fractal
x = 12, but the question is asking for $m\angle 3$
Dork9399
gj
alr
no ur right
yea