Me! a pharmacist has a 12% boric acid solution and a 20% boric acid solution. how much of each must he use to make 80 grams of a 15% boric acid solution?

x = amount of 20% solution needed
80 grams - x = amount of 12% solution needed

20% = 0.20

12% = 0.12

15% = 0.15

Write out the equation:
0.20x + 0.12(80-x) = 0.15(80)

Distribute the part in parenthesis:
0.20x + 9.6 - 0.12x = 12

Subtract 9.6 from each side and combine like terms:

0.20x - 0.12x = 12 - 9.6

0.08x = 2.4

Divide both sides by 0.08:
x = 2.4/0.08

x = 30 grams of the 20% solution

80 - 30 = 50 grams of the 12%