Consider the following situation: A couple decides that they want to raise at least one boy and one girl. They decide to keep having children until they have one child of each gender, and then stop having children. Assume that having a boy or a girl is equally likely, and assume that the gender of one child has no influence on the gender of the next.
The following listing gives the results of a simulation of the family size for 20 couples.
| Couple | Boys | Girls | Total |
|---|---|---|---|
| Couple 1 | 1 | 1 | 2 |
| Couple 2 | 1 | 2 | 3 |
| Couple 3 | 1 | 1 | 2 |
| Couple 4 | 2 | 1 | 3 |
| Couple 5 | 4 | 1 | 5 |
| Couple 6 | 1 | 1 | 2 |
| Couple 7 | 1 | 1 | 2 |
| Couple 8 | 1 | 1 | 2 |
| Couple 9 | 1 | 2 | 3 |
| Couple 10 | 1 | 1 | 2 |
| Couple 11 | 4 | 1 | 5 |
| Couple 12 | 1 | 2 | 3 |
| Couple 13 | 1 | 1 | 2 |
| Couple 14 | 1 | 4 | 5 |
| Couple 15 | 1 | 1 | 2 |
| Couple 16 | 2 | 1 | 3 |
| Couple 17 | 1 | 2 | 3 |
| Couple 18 | 1 | 2 | 3 |
| Couple 19 | 1 | 3 | 4 |
| Couple 20 | 1 | 2 | 3 |