How many quarts of pure antifreeze must be added to 3 quarts

How many quarts of pure antifreeze must be added to 3 quarts of a 10% antifreeze solution to obtain a 60% antifreeze solution? (Hint: pure antifreeze is 100% antifreeze.)

Solution

Let x quarts of pure antifreeze are added:

3 quarts of a 10% antifreeze --- 0.1*3 = 0.3

(x+0.3)/(x+3) = 0.6

(x+0.3) = 0.6x +1.8

0.4x = 1.5

x = 3.75 quarts of pure antifreeze