Multiple choice

A 45 litre mixture of spirit and water contains 20% of water in it. How much water must be added to it to make water 25% in the new mixture?

  1. 22 litres

  2. 5 litres

  3. 4 litres

  4. 3 litres
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Initial mixture: 45L, 20% water = 9L water, 36L spirit. Let x be water added. New water = 9+x, total = 45+x. (9+x)/(45+x) = 0.25. 9+x = 11.25 + 0.25x. 0.75x = 2.25. x = 3.

AI explanation

Using the method of mixtures and alligation, the initial mixture has 20% water and pure water has 100% concentration, while the desired target is 25%. Setting up the alligation gives the ratio of the initial mixture to added water as (100 minus 25) to (25 minus 20), resulting in 75 to 5 or 15 to 1. Since the initial 15 parts represent the 45 litres of the given mixture, 1 part of water equals 45 divided by 15, which is 3 litres.

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