Question

Julia is a chemistry student. She is working on an experiment for which she needs 10 liters of a 20% salt solution. All she has in her lab are a 10% salt solution and a 40% salt solution. She decides to mix these to make her own 20% solution. How much of the 40% solution will she need to use? Round your answer to the nearest tenth of a liter.

Answer 1

.1 x + .4 y = .2(x+y)
but x = 10-y

.1(10-y) + .4 y = .2x + .2y

1 - .1 y + .4 y = .2 (10-y) + .2 y
(.4-.1 +.2-.2)y = 1
3 y = 10
y = 10/3