Question

How many milliliters of a 12% alcohol solution and how many milliliters of a 30% alcohol solution must be mixed to obtain 72 ml of a 20% alcohol solution?

Answer 1

Target concentration = 20%.

Ratio of 12% and 30% alcohols needed

30-20 : 20-12 = 10:8 = 5:4

Volume of 12% = 72 mL * (5/(5+4)) = 40 mL

Volume of 30% = 72 mL *(4/(5+4)) = 32 mL

Total = 40+32 = 72 mL of 20%