Question

Pipe A can fill a tank in 30 mins and Pipe B can fill it in 28 mins. If 3/4th of the tank is filled by Pipe B alone and then both are opened, how much more time is required by both the pipes to fill the tank completely?

Answer 1

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Solution: 4
∵ In 28 minutes Pipe B Can Fill tank = 1

∴ In 1 minute Pipe B Can Fill tank = (1/28)

3/4 of the tank is filled in time = (3/4) ÷ (1/28) = 21 minutes

After 21 minutes The tank remaining empty = 1 - (3/4) = (1/4)

∵ In 30 minutes Pipe A Can Fill tank = 1

∴ In 1 minute Pipe A Can Fill tank = (1/30)

In 1 minute Pipe A + Pipe B can fill tank = (1/30) + (1/28) = (29/420) ................ (LCM of 28, 30 = 420)

∵ (29/420)th of Tank can be filled by Pipe A & Pipe B combined in time = 1 mins

∴ 1 Tank can be filled by Pipe A & Pipe B combined in time = 1 ÷ (29/420) mins

∴ (1/4) Tank can be filled by Pipe A & Pipe B combined in time = (1/4) ÷ (29/420) mins

= (420/116) = (105/29) = 3.62 Minutes

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