Question

In a two-child family, one child is a boy. What is the probability that the other child is a girl?

Answer 1

50%

Explanation:

When I flip a coin, it can come up heads or tails, with a 50/50 chance on each flip. The flips that came before don't influence the flip I'm about to do. If I flip a coin 10 times and the first 9 times it comes up heads, there is still a 50% chance that the 10th flip will be tails. The events that come before don't influence the current event.

That is the situation we have here. The fact that a family already has a boy does not change the odds that the other child will be a girl. And so the odds of the other child being a girl is 50%.