Sarah needs 10 cups of water for each cup of bleach.
To find out how many cups of water Sarah needs for each cup of bleach, we need to set up a proportion using the given information.
Sarah's mixture contains 20 cups of water and 2 cups of bleach. Let x be the number of cups of water needed for each cup of bleach.
The proportion will be: 20 cups / 2 cups = x cups / 1 cup. To solve for x, we can cross multiply and get: 20 cups * 1 cup = 2 cups * x cups.
Simplifying this gives us: 20 cups = 2x cups. Dividing both sides by 2, we find that x = 10 cups.
Therefore, Sarah needs 10 cups of water for each cup of bleach.