How many liters of a 65% alcohol solution must be added to 30 L of a 25% alcohol solution to produce a 40% alcohol solution

18

Step-by-step explanation:

Let's say x is the volume of the 65% solution.

Amount of alcohol in the 65% solution + amount of alcohol in the 25% solution = amount of alcohol in the 40% solution

0.65 x + 0.25 (30) = 0.40 (x + 30)

0.65 x + 7.5 = 0.40 x + 12

0.25 x = 4.5

x = 18

You need to add 18 liters of the 65% solution.