A 40-litre solution contains 30% alcohol. How many litres of pure alcohol must be added to make a solution that is 50% alcohol?
Answer and explanation
Correct answer: B. 16 litres
- Step 1: The original alcohol is 0.30 x 40 = 12 litres. Add x litres of pure alcohol.
- Step 2: 12 + x = 0.5(40 + x) leads to 12 + x = 20 + 0.5x, so 0.5x = 8 and x = 16.
Answer
16 litres.
Why not the others: The other values treat percentage points as litres or ignore that the total volume also grows.
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