Mix a solution that is 70% alcohol with a solution that is 10% alcohol to make 240 mL of a solution that is 20% alcohol. How much of each solution should you use?
A) So, mix 120 mL of the 70% solution and 120 mL of the 10% solution.
B) So, mix 30 mL of the 70% solution and 210 mL of the 10% solution.
C) So, mix 40 mL of the 70% solution and 200 mL of the 10% solution.
D) So, mix 210 mL of the 70% solution and 30 mL of the 10% solution.
E) So, mix 200 mL of the 70% solution and 40 mL of the 10% solution.

Question

Quizplus · Accepted Answer

Let x be the amount of the 70% solution and y be the amount of the 10% solution. Then we have two equations: 
x + y = 240 (total volume) 
0.7x + 0.1y = 0.2(240) (total amount of alcohol) 
Solving these equations, we get x = 40 and y = 200. Therefore, we need to mix 40 mL of the 70% solution with 200 mL of the 10% solution to make 240 mL of a solution that is 20% alcohol. Choice C is the best option.

Mix a Solution That Is 70% Alcohol with a Solution