Dr. Graham needs 30 L of a 50% acid solution to conduct an experiment. She only has a 60% acid solution and a

20% acid solution in her lab. How many liters of each solution should she mix together?

Let x be the amount in L of the 20% acid and y be the amount in L of the 60% acid. Doing an overall volume balance,

V = x + y = 30

Then, doing an alcohol balance,

0.2x + 0.60y = (30) (0.5)

The values of x and y from the generated equations above are

x = 7.5L

y = 22.5 L

Therefore, she will need 7.5L of 20% acid solution and 22.5L of 60% acid solution.