Q: A town has two hospitals, one big and one small. Every day the big hospital delivers 1000 babies and the small hospital delivers 100 babies. There's a 50/50 chance of male or female on each birth. Which hospital has a better chance of having the same number of boys as girls?

A: The small one. If there are 2N babies born, then the probability of an even split is

(2N choose N) / (2 ** 2N) ,

where (2N choose N) = (2N)! / (N! * N!) .

This is a DECREASING function.

If there are two babies born, then the probability of a split is 1/2 (just have the second baby be different from the first). With 2N babies, If there is a N,N-1 split in the first 2N-1, then there is a 1/2 chance of the last baby making it an even split. Otherwise there can be no even split. Therefore the probability is less than 1/2 overall for an even split.

As N goes to infinity the probability of an even split approaches zero (although it is still the most likely event).