Question

How many gallons of a 90% antifreeze solution must be mixed with 90 gallons of 20% antifreeze to get a mixture that is 80% antifreeze?

Answer 1

540 gallons of 90% antifreeze has to be mixed.

Solution:

First, I will set up my table. I will fill in the unknown with variable x.

The table is attached below

From this table, we can easily set up the two equations.

Sum of values of two solutions = Value of mixture

0.9x + 18 = 0.8(x + 90)

0.9x + 18 = 0.8x + 90 x 0.8

0.9x – 0.8x = 72 – 18

0.1x = 54

x = 540

Hence, 540 gallons of 90% antifreeze has to be mixed.