Paper 1 · Mathematical Reasoning and Aptitude
A mixture of 40 litres of milk and water contains 10% water. How much water should be added so that water becomes 20% of the new mixture?
A5 litres ✓ Correct
B4 litres
C6.5 litres
D7.5 litres
Correct answer: (A) 5 litres — 5 litres of water should be added, so that is the answer.
Explanation
★5 litres of water should be added, so that is the answer.
★In 40 litres, 10 per cent water is 4 litres, and milk is 36 litres.
★Let x litres of water be added, so the water becomes 4 plus x and the total becomes 40 plus x.
★For water to be 20 per cent, 4 plus x equals 0.2 times 40 plus x.
★So 4 plus x equals 8 plus 0.2x, giving 0.8x equal to 4.
★So x equals 5, meaning 5 litres of water should be added.
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