Question

You need a 75% alcohol solution. On hand, you have a 150 mL of a 50% alcohol mixture. You also have 90% alcohol mixture. How much of the 90% mixture will you need to add to obtain the desired solution?

Answer 1

250 mL

Explanation:

You want to know the amount of 90% alcohol solution you need to add to 150 mL of 50% solution to make a mix that is 75% alcohol.

Setup

Let x represent the amount of 90% solution needed. Then the amount of alcohol in the mix is ...

0.90x + 0.50(150) = 0.75(150 +x)

Solution

Simplifying, we have ...

0.90x +75 = 112.5 +0.75x

0.15x = 37.5 . . . . . . . subtract (75+0.75x)

x = 250 . . . . . . . . . . divide by 0.15

You need to add 250 mL of the 90% mixture to obtain the desired solution.

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