A container mixes 7 L of a 20% juice solution with 12 L of a 40% juice solution. How many litres of pure juice are in the mixture?

A) 67/10 L

B) 57/10 L

C) 31/5 L

D) 36/5 L

Answer: C

Explanation: Pure juice in each part equals its volume multiplied by its concentration.
7 × 0.20 + 12 × 0.40 = 31/5 L of pure juice.