Multiple choice

Pipe A can fill a tank in thrice the time in which pipe B can fill the same tank. If both the pipes work simultaneously, it takes 3 hours to fill the empty tank. In how many hours can A alone fill the tank? पाइप A एक टंकी को पाइप B द्वारा टंकी को भरने में लगे समय के तीन गुने में भर सकता है। यदि दोनों पाइप एक साथ चालू की जायें तो खाली टंकी को भरने में 3 घंटे लगते हैं। A अकेले टंकी को कितने घंटे में भर सकता है?

  1. 4 hours/ घंटे

  2. 6 hours/ घंटे

  3. 9 hours/ घंटे

  4. 12 hours/ घंटे
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D Correct answer
Explanation

Let B's time = t hours, so A's time = 3t hours. Together: 1/t + 1/(3t) = 1/3 (combined rate per hour). Solving: 4/(3t) = 1/3, so 3t = 12 and t = 4. Therefore A alone takes 12 hours. Verification: A fills 1/12 per hour, B fills 1/4 per hour, together 1/12 + 3/12 = 4/12 = 1/3 tank per hour, so 3 hours to fill. Standard work-rate problem.

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