Question: A container has 80 liters of a solution that is 10% acid. If 20 liters of this solution is replaced with pure acid, what will be the new concentration of acid in the solution?

Options:

1. 15%
2. 20%
3. 25%
4. 30%

Correct Answer: 25%

Solution:

Initial acid = 10% of 80 = 8 liters. After removing 20 liters, acid left = 8 - 2 = 6 liters. Adding 20 liters of pure acid gives 6 + 20 = 26 liters of acid in 80 liters. New concentration = (26/80) * 100 = 32.5%.