You are having a party. How much giner ale should be added to vodka(let's say 100% alcohol) in order to obtaoin 5 qyarts of 40% alcohol beverage?
The assumption of 100% alcohol content for the vodka is much too high. Did they tell you to assume that? Vodka is typically 40% to 50% alcohol.
If you start with X quarts of vodka and Y of ginger ale,
X + Y = 5
The alcohol content of the mixture should be 2 quarts. If the vodka is pure alcohol, X = 2 quarts and Y = 3 quarts. If it is 50% alcohol you need X = 4 quarts vodka and Y = 1 quart ginger ale.