A radiator contains 14 quarts of fluid 20 of which is antifr

A radiator contains 14 quarts of fluid, 20% of which is antifreeze. How much fluid should be drained and replaced with pure antifreeze so that the new mixture is 60%antifreeze? (Round your answer to two decimal places.)

Solution

Let x quarts of antifreeze replaced with pure antifreeze so that the new mixture is 60% antifreeze. then we get equation:

(100% of x) + (20% of (14-x)) = 60% of 14
1x+0.20(14-x)=0.60*14
1x+2.8-0.20x=8.4
0.80x+2.8=8.4
0.80x=8.4-2.8
0.80x=5.6
x=5.6/0.80
x=7
Hence answer is 7 quarts.