Multiple choice

Two pipes X and Y can fill a cistern in 6 hours and 10 hours respectively. Pipe Z can empty the tank in 4 hours. If all the three pipes are open then in how many hours the cistern will be full? दो पाइप X और Y क्रमशः 6 घंटे और 10 घंटे में एक टैंक भर सकते हैं। पाइप Z टैंक को 4 घंटे में खाली कर सकता है। यदि तीनों पाइप खुले हैं तो कितने घंटे में टैंक पूरा भर जाएगा?

  1. 30

  2. 45

  3. 50

  4. 60
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Combined rate = 1/6 + 1/10 - 1/4 = (10 + 6 - 15)/60 = 1/60 per hour. Time to fill = 1/(1/60) = 60 hours. Pipe X fills at rate 1/6, Y at 1/10, but Z empties at 1/4, so the net filling rate is very slow. Options A, B, and C underestimate the time.

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