Question

A scientist needs 10 liters of a 20% acid solution for an experiment, but she has only a 5% solution and a 40% solution. To the nearest tenth of a liter, about how many liters of the 5% and the 40% solutions should she mix to get the solution she needs?

Answer 1

5.714 liters of the 5% solution and 4.286 of the 40%.

Explanation:

Let x be the volume of 40% solution and y = volume of the 5% solution.

x + y = 10

0.40x + 0.05y = 0.20(x + y)

From the first equation x = 10 -y so we have:

0.40(10 - y) + 0.05y = 0.20( 10 - y + y)

4 - 0.40y + 0.05y = 2

-0.35y = -2

y = 5.714 liters of the 5%.

and x = 10 - 5.714 = 4.286 liters of the 40% solution.