Answer
$0.5$
Work Step by Step
We know that $probability=\frac{number \ of \ good \ outcomes}{number\ of\ all\ outcomes}$. There are 4 possibilities to have four kids: boy-boy, boy-girl, girl-boy, girl-girl. Therefore the probability of getting one of each sex (2 opportunities) is:$\frac{2}{4}≈0.5.$
