Question 385347

Here we firstly find the probability of event when all 25 people have different birthday...

  probability of first people have its own birthday = 365/365  ( sure )

  probability of second people have different b'day to first = 364/365
 
  probability of third people have different b'day to first and second = 363/365
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similarly for 25th person, probability of different b'day = 341/365


probability when all have different b'day P(A) = 365/365 * 364/365 *.....*341/365


   = (1/365)^24 * ( 364 *.....*341)  

   

now, probability that 2 or more people have common b'day = P(A')


= 1-P(A)