substitution method

Question

A chemist has an 80% alcohol solution and a 30% alcohol solution. How many liters of each should he use to obtain 5 liters of a 60% alcohol solution?

Answer 1

X+y = 5

0.8x + 0.3y = 0.6(5) = 3

0.8x + 0.3 ( 5 - x) = 3

0.8x + 1.5 - 0.3x = 3

0.5x = 1.5

x = 3

y=2