A Scientist needs 10 liters of a 20% acid solution for an experiment, but she only has 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?

In this question, you want to make 10 liters 20% concentration solution by mixing 5% and 40% concentration. There should be multiple answers to this question. Assuming that the total volume of 5% and 40% solution equal to 10L (no solution wasted), then you can determine the volume of solution needed. The formula should be:

if x would be the of volume 40% solution, then the volume of 5% would be:

10 L = 40% solution volume + 5% solution volume

10 L = x + 5% solution volume

5% solution volume = 10l-x

Then the volume calculation would be:

volume20%*concentration20% = volume40%*concentration40% + volume5%*concentration5%

10 liter * 20% = x liter*40% + (10 - x) liter*5%

10l * 20% = x liter * 35% + 10 liter*5%

x liter * 35 = 10l * 20 - 10l * 5 = 10l*15

x liter = 10l * 15/35 = 4.28 L = 4.3L

The volume of 40% solution = 4.3L

The volume of 5% solution = 10L - 4.3L = 5.7L