You need a 50% alcohol solution. On hand, you have a 250 mL of a 15% alcohol mixture. You also have 75% alcohol mixture. How much of the 75% mixture will you need to add to obtain the desired solution

350 mL

Explanation:

We need a 50% alcohol solution and we have 2 mixtures. One is 75% alcohol while the other is 15% alcohol.

Quantity of 15% alcohol is 250 mL.

Let quantity of 75% alcohol mixture be x.

Thus, we will produce;

0.5(x + 250)

Now, the reaction that will procuce this quantity is;

Sum of actual quantity of alcohol in each solution which is;

0.75x + 0.15(250)

Thus, equating both we have;

0.75x + 0.15(250) = 0.5(x + 250)

0.75x + 37.5 = 0.5x + 125

0.75x - 0.5x = 125 - 37.5

0.25x = 87.5

x = 87.5/0.25

x = 350 mL