Suppose a wall divides a playground, and twenty balls lie on the ground on the east side, while forty balls lie on the west side. If a child on the east side of the wall always tosses a ball over the wall at the same time a child on the west side tosses a ball over the wall, then:

The amount of balls on each side would stay the same. The amount of balls would stay the same as long as both sides are throwing the same number of balls at the same time.

Step-by-step explanation:

Equation for east side: 20 (balls) -1 (thrown over to west) + 1 (thrown over from west) = 20 balls

Equation for west side: 40 (balls) -1 (thrown over to east side) +1 (thrown over by east side) = 40 balls

step-by-step explanation: