Multiple choice

A vessel full of pure acid contains 10 litres of it, of which 2 litres are withdrawn. The vessel is then filled with water. Next 2 litres of the mixture are withdrawn, and again the vessel is filled up with water. The ratio of the acid left in the vessel with that of the original quantity is-

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

After first withdrawal: 8 litres acid remain. When 2 litres of this 80% acid mixture are removed, acid removed = 2 × 0.8 = 1.6 litres. Acid remaining = 8 - 1.6 = 6.4 litres. Original acid = 10 litres. Ratio = 6.4:10 = 16:25. Each withdrawal dilutes the mixture progressively, and the acid fraction follows the pattern (remaining volume/original volume) raised to the power of number of withdrawals.

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