SSC CGL (Prelims) General: Mixtures and Alligation questions with solutions

Q1. A container has 60 litres of a mixture of acid and water in the ratio 7:3. 20% of the mixture is taken out and replaced with water. This operation is repeated once more. What is the final percentage of acid in the mixture?

1. 44.8%
2. 51.2%
3. 53.7%
4. 56.8%

Answer: 44.8%

Initially, acid = 70% of 60 = 42 litres. Each time 20% of the mixture is removed and replaced with water, the acid left becomes 80% of the previous amount. After two such operations, acid = 42 × 0.8 × 0.8 = 26.88 litres. So the final percentage of acid = (26.88/60) × 100 = 44.8%.