Question: Bertha plays tennis. Every ten games, one of her tennis balls wears out. Every five games, she loses a ball. Every four games, she buys a canister of three balls. She started with two balls and gave one to her partner. After twenty games, how many tennis balls does she have? Think carefully first, then make a decision:
Bertha wears out 20 / 10 = 2 tennis balls in 20 games. She loses 20 / 5 = 4 tennis balls in 20 games. She buys canisters of 3 * 20 / 4 = 15 tennis balls in 20 games. Bertha started with 2 balls and gave 1 away, so she has 2 + 15 - 2 - 4 - 1 = 10 tennis balls after twenty games. So the answer is 10.