Multiple choice

A container has 30 L of water. If 3 L of water is replaced by 3 L of spirit and this operation is repeated twice , what will be the quantity of water in the new mixture?

  1. 27.1

  2. 25.5

  3. 14.4

  4. 24.3

  5. 22
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Initial: 30L water (0% spirit). After first replacement: 3L water removed, 3L spirit added → 27L water + 3L spirit. Water concentration = 27/30 = 0.9. Second operation: 3L of mixture removed containing 0.9 × 3 = 2.7L water and 0.3L spirit. Remaining: 27 - 2.7 = 24.3L water, 3 - 0.3 = 2.7L spirit. Add 3L spirit: Final = 24.3L water + 5.7L spirit = 30L total. Water quantity = 24.3L. Formula: Final water = 30 × (1 - 3/30)² = 30 × (0.9)² = 30 × 0.81 = 24.3L.

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