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What is the probability that in a group of 10 students at

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What is the probability that in a group of 10 students at [#permalink] New post 15 May 2004, 15:46
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What is the probability that in a group of 10 students at least 2 will have the same birthday?
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 [#permalink] New post 15 May 2004, 19:19
1- (365C10)/(365^10)

1 - P( that none will have the same birthday.)
Choose 10 different dates for all 10 of them from 365 days in 365C10 ways
Since each birth days can range from 1 to 365 and 10 such people are there total combinations = 365^10

Hi mrihaque

Your P value is > 1

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 [#permalink] New post 17 May 2004, 10:49
Prob of having different birthdays = 1*(364/365)*...*(356/365)

The answer = 1 - the above quantity = 1 - [365P10/365^10]
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 [#permalink] New post 17 May 2004, 12:33
I think anandnk is right as it would be C not P while picking up birthdates
so it would be 1 - (365C10/365^10)
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 [#permalink] New post 17 May 2004, 12:37
well, you are considering only one ordered sequence among 10! possibilities. As the students are different, one need to add the same probability 10! times. Then you'll end up with 360P10/365^10. It does not matter whether one uses C or P, but what matters is basic counting.
  [#permalink] 17 May 2004, 12:37
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