You need 210 mL of a 55% alcohol solution. On hand, you have a 70% alcohol mixture. How much of the 70% alcohol mixture and pure water will you need to obtain the desired solution?

Answer 1

210(.55) = .70x

x = 115.5/.7 = 165 mL of 70% solution

mixed with

210-165 = 45 mL of pure water

creates 210 mL of 55% solution

.7(165) = 1155 =.55(210)