Pipe A can fill a tank in 828 minutes and Pipe B can empty the same tank in 1035 minutes. If both pipes are opened together, how many hours will it take to fill the empty tank?

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UP Police SI (दरोगा) Official PYP (Held On: 28 Nov 2021 Shift 1)
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  1. 75
  2. 69
  3. 71
  4. 73

Answer (Detailed Solution Below)

Option 2 : 69
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UP Police SI (दरोगा) Official PYP (Held On: 2 Dec 2021 Shift 1)
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Detailed Solution

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Given:

Pipe A can fill the tank in 828 minutes

Pipe B can empty the tank in 1035 minutes

Formula used:

Total work = LCM of 828 and 1035

Efficiency = Work ÷ Time

Net efficiency = A's efficiency - B's efficiency

Time taken = Total work ÷ Net efficiency

Calculations:

LCM of 828 and 1035 = 4140 units (total work)

A's efficiency = 4140 ÷ 828 = 5 units/min

B's efficiency = 4140 ÷ 1035 = 4 units/min

Net efficiency = 5 - 4 = 1 units/min

Time = 4140 ÷ 1 = 4140 minutes

Convert to hours = 4140 ÷ 60 = 69 hours

∴ Time to fill the tank = 69 hours

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