Bunuel wrote:
Pipe A fills a tank of 700 litres capacity at the rate of 40 litres a minute. Another pipe B fills the same tank at the rate of 30 litres a minute. A pipe at the bottom of the tank drains the tank at the rate of 20 litres a minute. If pipe A is kept open for a minute and then closed and pipe B is kept open for a minute and then closed and then pipe C is kept open for a minute and then closed and the cycle repeated, how long will it take for the empty tank to overflow?
A. 14 minutes
B. 39 minutes
C. 40 minutes 20 seconds
D. 41 minutes 20 seconds
E. 42 minutes
Are You Up For the Challenge: 700 Level Questions Given informationPipe A fills the tank at 40 Litres/minute
Pipe B fills the tank at 30 Litres/minute
Pipe C empties the tank at 20 Litres/minute
The total capacity of the tank is 700 Litres
As per the information provided in the question stem, the tank will be filled by alternatively opening and closing
pipes A,B, and C. In a cycle of three minutes, the total influx into the tank is 50 litres(+40+30-20)
In 39(3*13) minutes, the tank has reached 650(50*13) litres of its capacity. In the next minute, Pipe A will
fill another 40 litres of water into the tank, making the total capacity 690 litres.
Now, Pipe B working at the speed of 30 litres/minute has to fill the remaining 10 litres, taking it 20 seconds to do so.
Therefore, with the cycle repeated, the empty tank to overflow in
40 minutes, 20 seconds(Option C)