#### Answer

$(2.1,.9)$

#### Work Step by Step

We are given that the midpoint $M$ of a line segment $PQ$ with endpoints ($x_{1}$,$y_{1}$) and ($x_{2}$,$y_{2}$) is equal to:
$M=(\frac{x_{1}+x_{2}}{2},\frac{y_{1}+y_{2}}{2})$
Therefore, $M=(\frac{2.5+1.7}{2},\frac{3.1+(-1.3)}{2})=(\frac{4.2}{2},\frac{3.1-1.3}{2})=(\frac{4.2}{2},\frac{1.8}{2})=(2.1,.9)$.