RRB NTPC CBT-1 previous year question
Pipes A and B can fill a tank in 12 hours and 15 hours, respectively. A third pipe C can empty the full tank in 20 hours. If A and B are opened together for 2 hours and then C is also opened, what is the total time taken to fill the tank?
Asked in RRB NTPC 2026 — 18 June Shift 2 · Quantitative Aptitude
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Correct answer: (D) 9 hours
In the first 2 hours, A and B together fill 2x(1/12+1/15) = 3/10 of the tank, leaving 7/10. With all three pipes open, the net rate is 1/12+1/15-1/20 = 1/10 per hour, so filling the remaining 7/10 takes 7 hours. Total time = 2+7 = 9 hours.
हिंदी में प्रश्न
पाइप A और पाइप B, किसी टंकी को क्रमशः 12 घंटे और 15 घंटे में भर सकते हैं। एक तीसरा पाइप ८, पूरी cpl का 20 Ue में खाली कर सकता Sl ACA ARB को एक साथ 2 Ue के लिए खोला जाए और फिर ० को भी खोल दिया जाए, तो टंकी को भरने में कुल कितना समय लगेगा?
उत्तर जाँचने के लिए किसी विकल्प पर टैप करें।
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सही उत्तर: (D) 8 घंटे
पहले 2 घंटों में A और B मिलकर टंकी का 2x(1/12+1/15) = 3/10 भाग भरते हैं, शेष 7/10 बचता है। तीनों पाइप खुले होने पर शुद्ध दर 1/12+1/15-1/20 = 1/10 प्रति घंटा है, इसलिए शेष 7/10 भरने में 7 घंटे लगते हैं। कुल समय = 2+7 = 9 घंटे।
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