Alaboratory technician needs to make a 108 -liter batch of a 20 % acid solution. how can the laboratory technician combine a batch of an acid solution that is pure acid with another that is 10 % to get the desired concentration?

The answer to this question would be:
100% solution= 12 liter
10% solution= 96 liter

In this question, you have 2 kinds of a solution with different concentration and try to make the third solution. To answer this question, you need to understand that you need to match the amount of the molecule. You can get the amount of molecule by multiplying the concentration with the volume. 
The calculation would be:
volume1+volume2= volume3
volume1 + volume2= 108l
volume1 = 108l - volume2

amount1 + amount 2 = amount3
volume1 * concentration1 + volume2 * concentration2 = volume3 * concentration3
volume1 * 100% + volume2 * 10% = 108 liter * 20%
volume1 + 1/10 volume2 = 21.6 liter
(108liter - volume2) + 1/10 volume2 = 21.6liter
108liter - 9/10 volume2- 21.6liter
108liter - 21.6 liter = 9/10 volume2
9/10 volume2= 86,4 liter
volume2= 96liter

volume1 = 108liter - volume2
volume1= 108 liter - 96 liter= 12 liter