Question

A druggist has two mixtures of a certain chemical and water, one containing 10% of the chemical and the other containing 40% of the chemical. How much of each mixture should he use to make 10 ounces that contain 25% of the chemical?
If x is the amount of 10% mixture used, then which expression represents the ounces of chemical contained in it?

Answer 1

Let x=amount of 10% and y=amount of 40%.  Since we are making 10oz total, y=10-x so we can say:

(.1x+.4(10-x))/10=.25

(.1x+4-.4x)/10=.25

4-.3x=2.5

-.3x=-1.5

x=5, and since y=10-x, y=5

So 5oz of 10% is mixed with 5oz of 40% to make 10oz of 25% solution.

check

(.1(5)+.4(5))/10=.25

(.5+2)/10=.25

2.5/10=.25

.25=.25