Multiple choice

200 litres of alcohol solution contains 30% alcohol. How much alcohol should be added to make it 50% in the solution?

  1. 40 L

  2. 60 L

  3. 80 L

  4. 50 L
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Initial alcohol = 30% of 200 = 60. Let x be added alcohol. (60 + x) / (200 + x) = 0.5. 60 + x = 100 + 0.5x. 0.5x = 40, x = 80.

AI explanation

By the method of alligation, the ratio of pure alcohol (100%) to the original solution (30%) to achieve a 50% concentration is (50 minus 30) to (100 minus 50), which is 20 to 50 or 2 to 5. The original solution is 200 litres, meaning 5 parts equals 200 litres and 1 part equals 40 litres. Since pure alcohol represents 2 parts, the amount to add is 80 litres.

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