My colleague Max Lummis became a father over the weekend, so in order to wrap up the recent series of posts on expected value, here’s a birth-themed, three-part math problem for your Monday afternoon.

I’ll give a hat-tip to the person who introduced me to the problem after posting the solution in a few days. Feel free to reference Wolfram and the rules of expectations.

Suppose there’s parents that can have infinite children who really want a boy. They will have kids until they have a boy. The probability of any given child being a boy is 50 percent.

- What is the expected number of boys?
- What is the expected number of girls?
- What is the expected percentage of the children that will be girls?