Antifreeze Problem

Question

How much pure antifreeze must be added to 12 gallons of 20% antifreeze to make a 50 % solution ?

Answer 1

12 * 0.2 + X = 0.5(X+12)

2.4 + X = 0.5X + 6

2.4 + X - 0.5X - 6 = 0

0.5X - 3.6 = 0

0.5 X = 3.6

5X = 36

X = 36/5 = 7.2

CHECK:

antifreeze: 7.2 + 2.4 = 9.6

altogether: 12+7.2 = 19.2

9.6 / 19.2 = 96/192 = 1/2 = 50%