Answer
$0.25$
Work Step by Step
We know that $probability=\frac{number \ of \ good \ outcomes}{number\ of\ all\ outcomes}$. Totally there are $2^{4}=16$ opportunities because every kid it can be either a boy or a girl. For us there are 4 possibilities where there is 1 boy, because the only boy can be either int the first, second, third or fourth place whilst the rest are girls. Therefore $probability=\frac{4}{16}=0.25.$
