How many liters of a 30% alcohol solution must be mixed with 90 liters of another 70% solution to obtain a 60% solution.

Let's call the number of liters of the 30% alcohol solution that you need to mix as "x." To solve this problem, you can set up an equation based on the concentration of alcohol in the mixtures: 0.30x + 0.70(90) = 0.60(x + 90) Now, let's solve for x: 0.30x + 63 = 0.60x + 54 Now, subtract 0.30x from both sides: 63 = 0.30x + 54 Subtract 54 from both sides: 9 = 0.30x Now, divide both sides by 0.30 to find the value of x: x = 9 / 0.30 x = 30 So, you need to mix 30 liters of the 30% alcohol solution with 90 liters of the 70% solution to obtain a 60% solution.