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Probability of age selection

  1. Sep 20, 2008 #1
    I have a question regarding a probability question. If four people are randomly selected what is the probability that at least one is born on my birthday. This would make me think that I want to do the formula of

    1 - (1/365)^4 which comes out to be
    1 - .000000000005636405776 = .999999999 which just doesn't seem right to me.

    I also have to do what is the probability that one is born on my birthday which makes me think that I want to do (1/365)^4

    Am I anywhere near the right path?
     
  2. jcsd
  3. Sep 20, 2008 #2

    HallsofIvy

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    (1/365)4 is the probability that all 4 were born on your birthday. 1- (1/365)4 is the probability that at least one was NOT born on your birthday.

    The probability that a given person was NOT born on your birth day is 364/365 (disregarding leap year). The probability that out of four people NONE of them was born on your birthday is (364/365)4 so the probability that at least one was born on your birthday is 1- (365/365)4. That's about 0.02.
     
  4. Sep 20, 2008 #3
    Thank you very much. That explanation cleared things up tremendously. It's an extremely easy concept but for some reason I'm having issues grasping it. Thanks again!
     
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