pearllx
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x~(8,p), if P(X=5)=P(X=6). Find the value of p.

idk how to do this..
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mqb2766
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(Original post by pearllx)
x~(8,p), if P(X=5)=P(X=6). Find the value of p.

idk how to do this..
Write the bold part in terms of p and solve.
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pearllx
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(Original post by mqb2766)
Write the bold part in terms of p and solve.
Sorry I don’t understand
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mqb2766
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(Original post by pearllx)
Sorry I don’t understand
Write the two binomial probabilities down for the 5th and 6th elements.
You've covered the binomials written using nCr at school?
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pearllx
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(Original post by mqb2766)
Write the two binomial probabilities down for the 5th and 6th elements.
You've covered the binomials written using nCr at school?
Yh but it was brief, so I do 8C5 and 8C6?
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mqb2766
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(Original post by pearllx)
Yh but it was brief, so I do 8C5 and 8C6?
Half correct. Why not read that section of your notes/book/google/... again.
http://www.a-levelmathstutor.com/sta...ribution02.php

If you don't understand the starting point, doing the question is a bit pointless.
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pearllx
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(Original post by mqb2766)
Half correct. Why not read that section of your notes/book/google/... again.
http://www.a-levelmathstutor.com/sta...ribution02.php

If you don't understand the starting point, doing the question is a bit pointless.
I understand it however I still don’t get how to solve for p
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mqb2766
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(Original post by pearllx)
I understand it however I still don’t get how to solve for p
What have you written down for the two probabilities?
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pearllx
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(Original post by mqb2766)
What have you written down for the two probabilities?
P(X=5) = 56p^5(1-p)^7

P(X=6) = 28p^6(1-p)^7
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mqb2766
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(Original post by pearllx)
P(X=5) = 56p^5(1-p)^7

P(X=6) = 28p^6(1-p)^7
The powers of p and (1-p) add up to n (8). The p ones are correct, but not the (1-p).
Also, sometimes it's easier to cancel down the nCr numbers leaving in factorial form, but in this case it makes little difference.
Last edited by mqb2766; 1 month ago
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pearllx
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(Original post by mqb2766)
The powers of p and (1-p) add up to n (8). The p ones are correct, but not the (1-p).
Also, sometimes it's easier to cancel down the nCr numbers leaving in factorial form, but in this case it makes little difference.
I thought so too but the formula said n-1 so I assumed the powers would be 7
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mqb2766
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(Original post by pearllx)
I thought so too but the formula said n-1 so I assumed the powers would be 7
Just look in your textbook. If you don't have one, get a copy. Many places online ...
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pearllx
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(Original post by mqb2766)
Just look in your textbook. If you don't have one, get a copy. Many places online ...
The website u sent me said the powers should be n-1 so I got confused
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mqb2766
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(Original post by pearllx)
The website u sent me said the powers should be n-1 so I got confused
There is one typo on there. Several others in that page give the correct one. If you were unsure it's easy to check. It would be 30s to look in your textbook, it would help you to get one.
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