Answer
$\frac{1}{2}log_{b}5$
Work Step by Step
We are given $log_{b}3=.5$ and $log_{b}5=.7$.
We know that $log_{b}x^{r}=rlog_{b}x$ (where $x$ and $b$ are positive real numbers, $b\ne1$, and $r$ is a real number).
Therefore, $log_{b}\sqrt 5=log_{b}5^{\frac{1}{2}}=\frac{1}{2}log_{b}5$.