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Please help with this probability question! cheers :-)

  • 06-12-2012 9:35pm
    #1
    aimsywamesy
    Registered Users, Registered Users 2 Posts: 8 ✭


    3 people are picked at random what's the probability that all 3 will have different birthdays.?
    NB take all months to be equally likely
    ans=55/72 please explain!


Comments

  • #2
    MathsManiac
    Registered Users, Registered Users 2 Posts: 1,595 ✭✭✭MathsManiac


    Are you sure you didn't take the question down wrongly?

    That is not the correct answer to the question asked. It is, however, the correct answer to the question "What is the probability that they were all born in different months?"

    To see this, first consider the total number of possible outcomes when three people are asked what month they were born in: 12*12*12.

    Next, consider how many of these outcomes we are interested in: 12*11*10 (second one can't be the same as the first; third can't be the same as either of the first two).

    So, assuming that all months are equally likely, and that the births of these three people are independent of each other, the answer is (12*11*10) / (12*12*12), which simplifies to 55/72.


  • #3
    aimsywamesy
    Registered Users, Registered Users 2 Posts: 8 ✭aimsywamesy


    yes you're right thank you!


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