Question

How many liters each of a 30% acid solution and a 50 % acid solution must be used to produce 70 liters of a 40 % acid solution? (Round to two decimal places if

necessary.)

Answer 1

30%: 35 liters

50%: 35 liters

Explanation:

The desired concentration is halfway between the concentrations of available solutions, so the mixture will be equal amounts of each.

35 liters of 30% acid and 35 liters of 50% acid must be used

_____

If you want to write an equation, it usually works well to let the variable represent the amount of the most concentrated constituent: 50% acid. Then the amount of acid in the final mix is ...

0.50x +0.30(70 -x) = 0.40(70)

0.20x +21 = 28 . . . . simplify

0.20x = 7 . . . . . . . . . subtract 21; next, divide by 0.20

x = 35 . . . . . . amount of 50% solution (liters)

70-x = 35 . . . amount of 30% solution (liters)