Two pipes, A and B, can fill a tank of 7800 litres in 12 hours and 10 hours, respectively. If they are opened together, how many hours will they take to fill an empty tank of 8800 litres?

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Question

This question was previously asked in

RRB NTPC Graduate Level CBT-I Official Paper (Held On: 05 Jun, 2025 Shift 3)

Answer 1

Given:

Pipe A can fill 7800 litres in 12 hours

Pipe B can fill 7800 litres in 10 hours

Total tank capacity to be filled = 8800 litres

Formula used:

Efficiency = Volume ÷ Time

Time taken together = Total volume ÷ (Efficiency of A + Efficiency of B)

Calculations:

⇒ A’s efficiency = 7800 ÷ 12 = 650 litres/hour

⇒ B’s efficiency = 7800 ÷ 10 = 780 litres/hour

⇒ Total efficiency = 650 + 780 = 1430 litres/hour

⇒ Time to fill 8800 litres = 8800 ÷ 1430

⇒ Time = \(\frac{8800}{1430} = \frac{880}{143} = \frac{80}{13}\)

∴ Required time = \(\frac{80}{13}\) hours.

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