Solution to: Boys and Girls
There are four possibilities for two children, with equal probabilities:
| first child: | second child: | |
| 1 | girl | girl |
| 2 | girl | boy |
| 3 | boy | girl |
| 4 | boy | boy |
The fourth possibility drops out, because Ronald and Michelle have a daughter (so either the first or the second child is a girl). Therefore, three possibilities remain, of which in one case the other child is also a girl. As a result, the probability is 1/3 (about 33%).
Back to the puzzle