Problem Set: Probability Problem 1: How many girls? Problem 1A: A...

Problem 1

1A. We list down all the possible scenarios when Mr. Q has at least two girls:
BGG, GBG, GGB, GGG
Hence there is 1/4 probability that MR. Q has three girls, given the statement that he has at least two girls.

1B. Similarly, we list down all the possible scenarios:
Case 1: There is only one girl born on May 13th. Then his other kid, let’s call R. Then R can be a boy (any birthday) or a girl not born on May 13th. If R is a boy, then total possible ways is 365 (since he can take any birthdays). On the other hand, if R is girl whose birthday is not May 13th, then total possible ways is 364. Without considering the order of birth, total ways is 365+364=729. When we take into consideration the order of birth, then total ways for this case is 729(2)=1458.