83. Given a parallelogram $A B C D$. Points $M$ and $N$ are the midpoints of sides $B C$ and $C D$ respectively. Find the ratio of the area of quadrilateral AM ND to the area of the parallelogram.
8.3. Given a parallelogram $A B C D$. Points $M$ and $N$ are the midpoints of sides $B C$ and $C D$ respectively. Find the ratio of the area of quadrilateral AMND to the area of the parallelogram.

Answer: $\frac{5}{8}$. Hint: Let $S_{\text {ABCD }}=S$. We have $S_{\text {ABM }}=\frac{1}{2} S_{\text {ABC }}=\frac{1}{4} S$. Further, $S_{\text {MCN }}=\frac{1}{4} S_{\text {BCD }}$ (since $M N$ is the midline in triangle $B C D$), so $S_{\text {MCN }}=\frac{1}{8} S$. Then $S_{\text {AMND }}=S-\frac{1}{4} S-\frac{1}{8} S=\frac{5}{8} S$.