Solution
= Solution
Let $S$ denote singing, and $M,F$ denote male and female. Equal population counts give $P(M)=P(F)=1/2$. The <law of total probability> therefore yields
$$
\boxed{P(S)=pP(M)+qP(F)=\frac{p+q}{2}}.
$$
= Solution
Let $S$ denote singing, and $M,F$ denote male and female. Equal population counts give $P(M)=P(F)=1/2$. The <law of total probability> therefore yields
$$
\boxed{P(S)=pP(M)+qP(F)=\frac{p+q}{2}}.
$$