Exams › SSC CGL (Prelims) › General

A container has a 100-litre mixture of acid and water in the ratio 4:1. 20 litres is removed and replaced with water. Then 20 litres is removed again and replaced with pure acid. What is the final percentage of acid?

1. 76.8%
2. 78.4%
3. 81.6%
4. 71.2%

Correct answer: 71.2%

Solution

Initially, acid = \(100 \times \frac{4}{5} = 80\) litres. After removing 20 litres of the mixture, acid removed = \(20 \times \frac{4}{5} = 16\), so acid left = 64 litres; then 20 litres of water is added, making acid still 64 litres in 100 litres. Next, 20 litres is removed again, so acid removed = \(20 \times \frac{64}{100} = 12.8\), leaving 51.2 litres acid; adding 20 litres pure acid gives 71.2 litres acid, i.e. 71.2%.

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