Bunuel wrote:

aiming4mba wrote:

Pipe A fills a tank of capacity 700 liters at the rate of 40 liters a minute. Another pipe B fills the same tank at the rate of 30 liters a minute. A pipe at the bottom of the tank drains the tank at the rate of 20 liters a minute. If pipe A is kept open for a minute and then closed and pipe B is open for a minute and then closed and then pipe C is open for a minute and then closed and the cycle is repeated, when will the tank be full?

In three minutes net gain is 40+30-20=50 liters;

After 13 cycles (13*3=39 minutes) net gain will be 13*50=650 liters.

Then in 1 minute pipe A will add 40 liters, 10 liters to be filled;

Then to fill 10 liters pipe B will need 10/30=1/3 min.

So total time \(39+1+\frac{1}{3}=40\frac{1}{3}\) min.

Why this process is not working for below?

https://gmatclub.com/forum/pipe-a-and-p ... 80611.htmlPipe A and Pipe B fill water into a tank of capacity 1000 litres at the rate of 100 litres/minute and 25 litres/minute respectively. Pipe C drains water from the same tank at the rate of 50litres/minute. Pipe A is kept open for a minute and then closed, then pipe B is kept open for a minute and then closed, followed by a drain pipe C for a minute and then closed. This process is repeated until the tank is full. How long will it take to fill the tank.

A) 39 mins

B) 40 mins

C) 39 mins and 20 secs

D) 37 mins

E) 41 mins

In three minutes net gain is 100+25-50=75 liters;

After 13 cycles (13*3=39 minutes) net gain will be 13*75=975 liters.

Then to fill 25 liters pipe A will need 25/100=1/4 min.

So total time \(39+\frac{1}{4}\) min = 39 min 15 sec

But Answer is D.

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Hasan Mahmud