Pipes A and B can fill a tank in one hour and two hours respectively while pipe C can empty the fill...........

Quantitative Aptitude (CGL) Pipes&cistern

Pipes A and B can fill a tank in one hour and two hours respectively while pipe C can empty the filled up tank in one hour and

fifteen minutes. A and C are turned on together at 9 a.m. After 2 hours, only A is closed and B is turned on. When will the tank

be emptied?

This questions was previously asked in

SSC CGL 6 June 2019 Shift-1

11:30 am.

12:10 pm.

12:20 pm.

10:30 am.

- Pipe A can fill the tank in 1 hour, so its rate is 1 tank per hour.

- Pipe B fills in 2 hours, so it fills at 0.5 tanks per hour.

- Pipe C empties the tank in 1 hour 15 minutes, or 1.25 hours, so it empties at a rate of -0.8 tanks per hour.

- At 9 a.m., Pipes A and C run together.

- They fill at a rate of 1 tank per hour and empty at -0.8 tanks per hour, so net rate is 0.2 tanks per hour.

- After 2 hours (11 a.m.), 0.4 tank is still filled since 2 x 0.2 = 0.4.

- Pipe A is now closed, and Pipe B opens, so B fills at 0.5 tanks per hour.

- Net fill rate now is 0.5 - 0.8 = -0.3 tanks per hour.

- 0.4 tank still needs emptying at this rate, which takes 0.4/0.3 = 4/3 hours (1 hour 20 minutes).

- Adding 1 hour 20 minutes to 11 a.m. results in 12:20 p.m.

12:20 pm is the correct answer.

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