Question

Chandra has 2 liters of a 14% solution of sodium hydroxide in a container. What is the amount and concentration of sodium hydroxide solution she must add to this in order to end up with 7 liters of a 34% solution?

Answer 1

Since you have 7 liters in all you know that 7 minus 2 is 5.

2*14% + 5*x% = 7*34%
0.28 + 5*x% = 2.38
5*x% = 2.38 - 0.28
5*x% = 2.10
x% = 0.42
x = 42%

Chandra must add 5 liters of 42% solution.