You need 510 mL of a 15% alcohol solution. On hand, you have a 85% alcohol mixture. How much of the 85% alcohol mixture and pure water will you need to obtain the desired solution?

Answer 1

.15(510) = .85x + 0(510-x)

.85x = 76.5

x = 76.5/.85 = 90 mL of 85% alcohol

and 510-90 = 420 mL of pure water

water is within 15 of 15%

85% is within 70 of 15%

70/15 = 14/3

420/90 = 14//3