Multiple choice

A pipe fills a tank in 10 hours. While another pipe empty that tank in 12 hours. If the pipes are opened alternatively by one hour then in how many hours the empty tank will fill ?/ एक नल किसी टंकी को 10 घंटे में भरता है जबकि दूसरा नल उसे 12 घंटे में खाली करता है। यदि खाली हौज में दोनों नलों को बारी-बारी से एक-एक घंटे के लिए खोला जाय तो हौज कितने घंटे में भर जायेगा ?

  1. 108 hrs/घंटे

  2. 110 hrs/घंटे

  3. 115 hrs/घंटे

  4. 109 hrs/घंटे
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

First pipe fills at 1/10 per hour, second empties at 1/12 per hour. In 2-hour cycle, net fill = 1/10 - 1/12 = 1/60. After 108 hours (54 cycles), tank has 54/60 = 9/10 filled. In 109th hour, first pipe fills another 1/10, completing it. Total time = 108 + 1 = 109 hours. Verification: 109 hours works correctly.

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