A 25 litre mixture contains 40% alcohol. How many litres of pure alcohol must be added to make the mixture 50% alcohol?
Correct answer B. 5 litres
Explanation
Alcohol = 10 litres. (10 + x) / (25 + x) = 1/2 gives 20 + 2x = 25 + x, so x = 5 litres.
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