Problem #PRU-5206

Problem

A quadrilateral $ABCD$ is given. Points K and L belong to the side $AB$ and $AK=KL=LB$ and points $N$ and $M$ belong to the side $CD$ and $CM=MN=ND$. Show that the area of the quadrilateral $KLMN$ is $\frac{1}{3}$ of the area of the quadrilateral $ABCD$.