12. Solve the following problem, from the “Ask Marilyn” column of Parade Magazine, October 29, 2000.

I recently returned from a trip to China, where the government is so concerned about population growth that it has instituted strict laws about family size. In the cities, a couple is permitted to have only one child.

In the countryside, where sons traditionally have been valued, if the first child is a son, the couple may have no more children. But if the first child is a daughter, the couple may have another child. Regardless of the sex of the second child, no more are permitted. How will this policy affect the mix of males and females?

To pose the question mathematically, what is the probability that a randomly selected child from the countryside is a boy?