Question

You need a 70% alcohol solution. On hand, you have a 40 mL of a 35% alcohol mixture. You also have 75% alcohol mixture. How much of the 75% mixture will you need to add to obtain the desired solution?

Answer 1

250 ml of the 75% mixture are needed to obtain the desired solution.

Explanation:

Since I need a 70% alcohol solution, and on hand, I have a 40 mL of a 35% alcohol mixture, and I also have 75% alcohol mixture, to determine how much of the 75% mixture will you need to add to obtain the desired solution, the following calculation must be performed:

100 x 0.75 + 0 x 0.35 = 75

90 x 0.75 + 10 x 0.35 = 71

89 x 0.75 + 11 x 0.35 = 70.6

87.5 x 0.75 + 12.5 x 0.35 = 70

12.5 = 40

87.5 = X

87.5 x 40 / 12.5 = X

3,500 / 12.5 = X

280 = X

Therefore, 250 ml of the 75% mixture are needed to obtain the desired solution.