Multiple choice

Two pipes can fill a cistern separately in 24 minutes and 40 minutes respectively. A waste pipe can drain off 30 litre per minute. If all the three pipes are opened, the cistern fills in one hour. The capacity (in litres) of the cistern is-

  1. 800

  2. 400

  3. 600

  4. 500
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Combined rate = 600/60 = 10 L/min. Fill rates: 600/24 = 25 L/min and 600/40 = 15 L/min. Waste pipe = 30 L/min (draining). Combined: 25 + 15 - 30 = 10 L/min ✓. For 60 minutes: 10 × 60 = 600 L. The cistern capacity is 600 litres.

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