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    Question

    A solution contains 30% alcohol and the rest water. If

    there are 20 litres of this solution, how many litres of water must be added to make the alcohol 20% in the new mixture?
    A 10 litres Correct Answer Incorrect Answer
    B 20 litres Correct Answer Incorrect Answer
    C 17 litres Correct Answer Incorrect Answer
    D 33 litres Correct Answer Incorrect Answer

    Solution

    Alcohol in original solution = 30% of 20 = 0.30 × 20 = 6 litres Let x litres of water be added. Total volume = 20 + x litres Alcohol remains 6 litres We want alcohol to be 20% of new mixture: 6 = 20% of (20 + x) 6 = (20/100) × (20 + x) 6 = (1/5)(20 + x) Multiply by 5: 30 = 20 + x x = 10 litres Answer: 10 litres of water

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