You need 120 mL of a 65% alcohol solution. On hand, you have a 60% alcohol mixture. How much of the 60% alcohol mixture and pure alcohol will you need to obtain the desired solution?

Answer 1

Let x = amount of the 60% solution

then

{ 60x + 100(120-x) }/(x + 120 - x) = 65

Solving for x:

40x = 4200

or x = 105 ml (the amount of the 60% solution

120-x = 15 ml (the amount of the pure alcohol)