Every ten games, Bertha's tennis ball wears out, so after twenty games, she would have worn out 20/10 = 2 tennis balls.
Every five games, she loses a ball, so after twenty games, she would have lost 20/5 = 4 tennis balls.
Every four games, she buys a canister of three balls, so after twenty games, she would have bought 20/4 = 5 canisters of three balls.
Each canister contains three balls, so after buying 5 canisters, she would have 5 x 3 = 15 new tennis balls.
Bertha started with two balls and gave one to her partner, so she would have 2 - 1 = 1 ball left.
In total, Bertha would have 1 + 15 - 2 - 4 = 10 tennis balls.
#### 10
The answer is: 10
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
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?

### Answer:
