There are two chemicals which do not react with each other. A container contains 10 litres of the chemical A. One litre of this c…

Question

There are two chemicals which do not react with each other. A container contains 10 litres of the chemical A. One litre of this chemical is removed from it and one litre of the chemical B is poured. Then one litre of the mixture is removed from the container and one litre of B is poured. If this process of replacing one litre of the mixture by one litre of B is performed once more, then what is the volume of B that is present in the container approximately (in percentage)?

1. A. 25
2. B. 27 (Correct answer)
3. C. 29
4. D. 31

Correct Answer

Option B — 27

Detailed Solution & Explanation

The correct answer is Option B (≈27%).

Key Points

• Each replacement leaves 9/10 of chemical A. After three replacements, A remaining = 10 × (9/10)³ = 10 × 0.729 = 7.29 litres.
• So B present = 10 − 7.29 = 2.71 litres ≈ 27%.

Additional Information

• The standard "replacement" formula (fraction retained = (1 − 1/V)ⁿ) gives Option B.