A chemist is mixing a 30% salt solution with a 15% salt solution to make 45 L of a new solution that will contain 25% salt. How much of the 30% solution should the chemist use?

Question

A chemist is mixing a 30% salt solution with a 15% salt solution to make 45 L of a new solution that will contain 25% salt. How much of the 30% solution should the chemist use?

Answer 1

There are a couple of ways to approach this problem.

First, is alligation. If not familiar with this approach, you can look it up.

HAVE.......WANT.......PARTS

30%..............................10 parts

.................25%.........................

15%.............................5 parts

Total parts = 15 = 45 L

1 part = 3 L

Thus, 30 L of 30% + 15 L of 15% ==> 45 L of 25%

The 2nd approach is algebraic.

(x L)( 30%) + (45 - x L)(15%) = (45 L)(25%)

30x + 675 - 15x = 1125

15x = 450

x = 30 L of 30% + 15 L of 15%