13. (3 points) As shown in the figure: In parallelogram $A B C D$, $O E=E F=F D$. The area of the parallelogram is 240 square centimeters, and the area of the shaded part is $\qquad$ square centimeters.
13. (3 points) As shown in the figure: In parallelogram $A B C D$, $O E=E F=F D$. The area of parallelogram $A B C D$ is 240 square centimeters, and the area of the shaded part is 20 square centimeters.
【Solution】Solution: Since in parallelogram $A B C D$, $A C$ and $B D$ are diagonals, dividing the area of parallelogram $A B C D$ into 4 equal parts, and the area of the parallelogram is 240 square centimeters,
thus $S \triangle D O C=240 \div 4=60$ (square centimeters),
also, since $\triangle O C E, \triangle E C F, \triangle F C D$ and $\triangle D O C$ have the same height, and $O E=E F=F D$,
thus $S \triangle E C F=\frac{1}{3} S \triangle D O C=\frac{1}{3} \times 60=20$ (square centimeters),
therefore, the area of the shaded part is 20 square centimeters.
The answer is: 20.