Multiple choice

15 litres of milk is drawn off by Surabhi from a container of milk and replaced it with same quantity of water. She again repeated the same process. Thus in three attempts the ratio of milk and water becomes 343: 169, the initial amount of milk in the container was -

  1. 120 l

  2. 121 l

  3. 125 l

  4. 145 l
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Each operation removes 15L milk and adds 15L water. After 3 operations, milk remaining = V*(1-15/V)^3 where V is initial volume. Water remaining = V - milk remaining. Ratio milk:water = 343:169, so milk/total = 343/512. Thus (1-15/V)^3 = 343/512, giving 1-15/V = 7/8, so V = 120L.

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