A couple plans on having 2 children. Given that at least one of them is a boy, the probability that both are boys is
$ \frac{P(both~boys)}{P(at~least~one~is~a~boy)} = \frac{0.25}{0.75} =\frac{1}{3} $
Furthermore, a textbook I am reading claims that the probability of both children being boys given that at least one is a boy born in spring is $\frac{7}{15}$. It doesn't explain its solution.
Why? What does the season have anything to do with whether both children are boys?