Multiple choice

A mixture of 60 litres contains milk and water in ratio 3 : 1. How many litres of mixture must be replaced with water so that the new ratio is 1 : 1?

  1. 10 litres

  2. 20 litres

  3. 15 litres

  4. 30 litres
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Initial mixture: 60L with milk:water = 3:1, so milk = 45L, water = 15L. Let x litres be replaced with water. After removing x litres (keeping ratio 3:1), milk removed = 3x/4, water removed = x/4. Remaining: milk = 45 - 3x/4, water = 15 - x/4. Adding x litres water: milk = 45 - 3x/4, water = 15 - x/4 + x = 15 + 3x/4. New ratio 1:1 means milk = water, so 45 - 3x/4 = 15 + 3x/4. Solving: 30 = 6x/4, so x = 20 litres.

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