Multiple choice

From 5 litre of 20% solution of alcohol in water. 2 litres of solution is taken out and 2 litres water is added to it. The strength of the alcohol in new solution is :

  1. 12 %

  2. 15 %

  3. 17 %

  4. 20 %
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A Correct answer
Explanation

Initial: 5L of 20% alcohol = 1L alcohol + 4L water. Removing 2L removes 0.4L alcohol (20% of 2L), leaving 0.6L alcohol in 3L solution. Adding 2L water gives 0.6L alcohol in 5L total. Strength = 0.6/5 = 0.12 = 12%. Key insight: removal is proportional to concentration.

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