What is the probability that a family of 2 children has no boys?

Answer 1

There is a One in two chance that the first child is a girl (not a boy), then there is the same chance (1/2) that the second child is not a boy. The chance that neither is a boy is (1/2) * (1/2) = 1/4.

Another way to look at it is like a table or grid. There are four possibilities, represented by the grid. The rows represent the sex of the first child, and the columns the second child. Where they intersect is the combination of the two. So you want any square where there are no boys (both girls). So there is only 1 square out of the 4 where this is true (denoted by a Y for Yes, the others denoted by n for no):

* | B | G |

B | n | n |

G | n | Y |