Question

A scientist mixes water (containing no salt) with a solution that contains 20% salt. She wants to obtain 140 ounces of a mixture that is 5% salt. How many ounces of water and how many ounces of the 20% salt solution should she use?

Answer 1

Let x represent ounces of water.
Ounces of 30% salt solution required = 140 - x

(Percentage of salt solution)(ounces of 30% solution required) = (5% salt solution needed)(extra salt solution needed)

(20/100)(140-x) = (5/100)*140
(1/5)(140-x) = (1/20)*140
28-1/5x = 7
Multiply both sides of the equation by 5 to isolate x:
5*(28-1/5x = 7)*5
140-x = 35
-x = 35 - 140
-x = -105
x = 105

Ounces of salt solution = 140 - 105 = 35

Therefore, 105 ounces of water is required and 35 ounces of salt solution is required