Algebra word problems

Question

A chemist has one solution that is 50% sulfuric acid and another that is 20% sulfuric acid. How many liters of each should she use to make 12 liters of a solution thats 30% sulfuric acid?

Answer 1

Assume x liters of 50% and 12-x liters of 20%.  Set up the solution as a weighted combination of the mixtures, weighted by the percentages.

 

50x + 20(12 - x) = 30(12)

 

Solve for x, get 12 - x, and finish from here.