Question

How many liters of 80% alcohol solution and 30% alcohol solution must be mixed to obtain 15 liters of 50% alcohol solution?

Answer 1

set up a table (multiply across and add down - don't add the middle column). Use the equation created by the "Total" row to solve for the variable.

Quantity (times) % equals Total

Sol'n 1: x * .80 = (x)(.8)

Sol'n 2: 15 - x * .30 = (15 - x)(.3)

Total: 15 * .50 = .8x + .3(15 - x)

15(.5) = .8x + 4.5 - .3x

7.5 = .5x + 4.5

3.0 = .5x

6 = x

Answer: 6 liters of 80% and 9 liters of 30%