Answer:
350 mL
Step-by-step explanation:
Let q represent the quantity (in mL) needed of the 70% solution. Then the total amount of mixture will be q+50 milliliters. The total amount of alcohol in the mixture will be ...
0.70q +0.30(50) = 0.65(50 +q)
.05q = 17.5 . . . . . . subtract (0.65q +1.50)
q = 350 . . . . . . . . . divide by 0.05
You will need 350 mL of the 70% solution.