Answer:
You will need
280 mL of the 60% solution
and 40 mL of pure alcohol.
Step-by-step explanation:
Let 'x' be the amount of 60% alcohol solution and y the amount of pure alcohol.
Therefore:
(0.6x + y)/320 = 0.65 ⇒ 0.6x + y = 208
x + y = 320
Solving the sistem of equations:
x = 280 and y = 40
Therefore, You will need
280 mL of the 60% solution
and 40 mL of pure alcohol.