Discovering that your three best friends were all born on a Sunday?
For a sample space of 400 years,
there are 97 leap years
So, probability of getting a leap year = 97/400= 0.2425
For a leap year(366 days),
Probability of 53 Sunday's = 2/7
Probability of 52 Sunday's = 5/7
For non leap year(365 days),
probability of 53 Sunday's = 1/7
Probability of 52 Sunday's = 6/7
Required probability that three best friends were all born on Sunday's = 0.2425* ((5/7)*(52/366)3 +(2/7)*(53/366)3)+ 0.7575*((6/7)*(52/365)3+(1/7)*(53/365)3)
= 0.2425*0.002916 + 0.7575*0.0029158476
=0.247624754 = 0.247625
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