jmc

Let there be $B$ boys and $G$ girls. Since every member is either a boy or a girl, $B+G=26$. Also, we have $\frac{1}{2}G+B=16$. Subtracting the second equation from the first, we have:

$\frac{1}{2}G=26-16=10⟹G=20$.

Thus there are $\boxed{20}$ girls on the chess team.