Question

How many gallons of a 20% antifreeze solution and a 15% antifreeze solution must be mixed to obtain 30 gal of a 18% antifreeze solution? Round to the nearest gallon

Answer 1

20% antifreeze solution = 18 gal

15% antifreeze solution = 12 gal

Explanation:

Let

20% antifreeze solution = x

15% antifreeze solution = y

x + y = 30

0.20x + 0.15y = 30 * 0.18

0.20x + 0.15y = 5.4

x + y = 30 (1)

0.20x + 0.15y = 5.4 (2)

From (1)

x = 30 - y

Substitute x = 30 - y into (2)

0.20x + 0.15y = 5.4 (2)

0.20(30 - y) + 0.15y = 5.4

6 - 0.20y + 0.15y = 5.4

- 0.20y + 0.15y = 5.4 - 6

-0.05y = -0.6

y = -0.6/-0.05

y = 12 gal

Substitute y = 12 into (1)

x + y = 30 (1)

x + 12 = 30

x = 30 - 12

x = 18 gal

20% antifreeze solution = 18 gal

15% antifreeze solution = 12 gal