Question

Two pipes can fill a cistern separately in $24min$ and $40min$ respectively. Waste pipe is opened which can drain the cistern at $30liters/minute$. If all the pipe are opened together then the cistern fills in one hour. The capacity (in litre) of the cistern is?

• A. $800$
• B. $400$
• C. $600$
• D. $500$
• E. None of these

Answer 1

The correct option is C $600$

The pipe A can fill in 24 minutes
the pipe B can fill in 40 minutes
and the pipe C can empty in x minutes.
24+40−x=60124+140−1x=160 [given]
1x=124+140−160=5+3−212=6120=1201x=124+140−160=5+3−212=6120=120
C can empty in 20 minutes.
In one minute, 'C' can waste 30 litres of water.
Capacity of the tank = 20×3020×30 = 600 litres.