You need a 10% alcohol solution. On hand, you have a 935 mL of a 5% alcohol mixture. You also have 95% alcohol mixture.

Question

How much of the 95% mixture will you need to add to obtain the desired solution?

Answer 1

Use a weighted average: Let x = amount of 95% alcohol added

{ (935)(5%) + x(95%) }/(935 + x) = 10% the % will cancel, so, we have

4675 + 95x = 9350 + 10x or

85x = 4675 so, x = 4675/85 = 55 ml of 95% alcohol added.