In $\Delta PQR$,M and N are points on sides PQ and PR respectively such that PM=15 cm and NR=8 cm .If PQ=25 cm and PQ=20 cm ,then MN is ______ QR.

Question

$\begin{array}{1 1}\text{parallel to}\\\text{perpendicular to}\\\text{half of}\\\text{none of these}\end{array}$