Marie mixes 20 liters of 12% acid solution with a 36% acid solution to make a 20% acid solution.

How many liters of 36% solution did she use?

10 liters

12 liters

13.7 liters

16 liters

Marie has two solution of the same acid with different concentration

Solution A 12% - 20 liters

Solution B 36% - Unknown

And she wants to obtain a new solution C with at 20%

According to the proporcionality of the dissolution In mathematical terms will can write the following equation:

quantity of A * concentration A + quantity o B * concentration B = (qty A + qty B) * concentration C

20*0.12 + x*0.36 = (20+x) * 0.2

being x the unknown quantity of the solution B solving the equation:

2.4 + x*0.36 = 4 + x*0.2

x*0.36 - x*0.2 = 4 - 2.4

x*0.16 = 1.6

x = 1.6/0.16 = 10

So the volume of solution B at 36% is 10 liters