Multiple choice

How much water should be added to 30 litres solution of water and alcohol, containing 90% alcohol, so as to reduce the content of alcohol to 80%?

  1. 3.5 litres

  2. 2.75 litres

  3. 6.5 litres

  4. 3.75 litres

  5. 3.25 litres
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Initial alcohol = 90% of 30 = 27 liters. Let x be the water added. New total = 30 + x. We want 27 / (30 + x) = 0.80. 27 = 24 + 0.8x, so 3 = 0.8x, x = 3.75 liters.

AI explanation

The initial 30 litre solution contains 90% alcohol, so there are 27 litres of alcohol and 3 litres of water. Let x be the amount of water added to achieve an 80% alcohol concentration, giving the equation 27 / (30 + x) = 0.80. Solving for x gives 27 = 24 + 0.8x, which simplifies to 3 = 0.8x. Therefore, x = 3.75 litres of water must be added.

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