Question

To make lemonade, I use a ratio of $7$ parts water to $1$ part lemon juice. If I want to make a gallon of lemonade, and there are four quarts in a gallon, how many quarts of water do I need

Answer 1

3 1/2 quarts

Explanation:

The fraction of the lemonade that is water can be determined from the ratio of water to lemon juice. That fraction of a gallon is the quantity of interest.

Water fraction

Of the 7+1 = 8 parts that make up the lemonade, 7 of those are water. That is, water is 7/8 of the lemonade.

Water quantity

Of the 4 quarts of lemonade, the quantity that is water will be ...

(7/8)(4 quarts) = 7/2 quarts = 3 1/2 quarts . . . of water