Multiple choice

A vessel contains 20 liters of acid. 4 liters of acid is taken out of the vessel and replaced by the same quantity of water. Next 4 liters of the mixture are withdrawn, and again the vessel is filled with the same quantity of water. Find the ratio of the quantity of acid left in the vessel to the quantity of acid initially in the vessel.

  1. $4 : 5$
  2. $4 : 25$
  3. $16 : 25$
  4. $1 : 5$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

After first replacement: Acid remaining = 20 - 4 = 16 liters (20 × 4/5). After second replacement: 4 liters of mixture removed, containing (16/20) × 4 = 3.2 liters acid. Acid remaining = 16 - 3.2 = 12.8 liters. Ratio of final to initial acid = 12.8 : 20 = 128 : 200 = 16 : 25. This is equivalent to (4/5)² after 2 operations.

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