Question

How many quarts of pure antifreeze must be added to 8 quarts of a 40% antifreeze solution to obtain a 60% antifreeze solution

Answer 1

Let q be the number of quarts of pure antifreeze that needs to be added to get the desired solution.

8 quarts of 40% solution contains 0.40 × 8 = 3.2 quarts of antifreeze.

The new solution would have a total volume of 8 + q quarts, and it would contain a total amount of 3.2 + q quarts of antifreeze. You want to end up with a concentration of 60% antifreeze, which means

(3.2 + q) / (8 + q) = 0.60

Solve for q :

3.2 + q = 0.60 (8 + q)

3.2 + q = 4.8 + 0.6q

0.4q = 1.6

q = 4