Single correct option
A vessel contains 80 litres of pure milk. 20 litres of milk is drawn off and replaced with water; the vessel is mixed well. Then 20 litres of this mixture is drawn off and again replaced with water. How many litres of milk remain in the vessel?
- A. 40 litres
- B. 42 litres
- C. 45 litres
- D. 48 litres
Show answer and solution
Answer: (C) 45 litres
After the first replacement, milk left = 80 × (60/80) = 60 litres (since 20 of 80 litres, i.e., 1/4, is removed and the fraction of milk retained each time is (80−20)/80 = 3/4). After the second replacement, milk left = 60 × (3/4) = 45 litres. General formula: milk remaining = 80×(3/4)² = 80×9/16 = 45.
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