Question

A doctor prescribes an ointment that is 4% hydrocortisone. A pharmacist has 1% and 5% concentrations in stock. How many ounces of each should the pharmacist use to make a 3-ounce tube?

Answer 1

If x oz. of 1% are used, then the rest (3-x) are 5%, so

.01x + .05(3-x) = .04(3)
x = 3/4

So, 3/4 oz of 1% and 9/4 oz of 5%

Note that 4% is 3/4 of the way from 1% to 5%, so 3/4 of the total is the 5% strength.

Answer 2

What if it was 2% instead of 4%?