For each side of a square, we draw semicircles that intersect each other at the center of the square. What is the area of the resulting four-leaf clover if one side of the square is $a$?
Let the center of the square $ABCD$ be $O$. If we subtract the area of the triangle $ABO$ from the area of the semicircle drawn over the side $AB$, we get the area of two half-leaves. Therefore, the area of the whole four-leaf clover is

$$
T=4\left(\frac{a^{2}}{8} \pi-\frac{a^{2}}{4}\right)=\frac{a^{2}}{2}(\pi-2)
$$

(Lipót Schnabel, Györ.)

The problem was also solved by: Bauer E., Dénes M., Erdős V., Fried E., Koffler B., Neumann L., Spitzer L., Steiner L., Szántó L., Szilárd V., Vilcsek A., Viola R.