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A vessel of capacity 90 litres is fully filled with pure milk. Nine litres of milk is removed from the vessel and replaced with water. Nine litres of the solution thus formed is removed and replaced with water. Find the quantity of pure milk in the final milk solution?

Correct answer: B. 72.9

  • A. 72
  • B. 72.9
  • C. 73.8
  • D. 74.7
  • E. None of these

Explanation

Each replacement removes 9 litres from a 90-litre vessel, so 81/90 = 0.9 of the milk remains after each operation. After two operations, pure milk remaining is 90 litres x 0.9 x 0.9 = 72.9 litres. The likely mistake is option a, 72 litres, from subtracting 18 litres of pure milk without accounting for the diluted solution removed second.

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