Question

Pipe 'A' can fill a tank in 15 hrs while a pipe 'B' can fill the tank in 20 hours and another pipe 'C' can empty the full tank in 30 hours. If all are opened together how long it will take to fill the tank.

• A. 3¼
• B. 5 3/4
• C. 6 2/3
• D. 7 2/3

Answer 1

Answer:

C. 6 2/3

In 1 hr A and B can fill (1/15) & (1/20) of the tank respectively and C can drain (1/30) of the tank in 1 hr. Net effect is that[ (1/15)+(1/20)-(1/30)]of the tank is filled in an hour, if all the pipes are opened so (4+3+2)/60 = 9/60 of the tank is filled Time taken by A, B & C to fill the tank. =(1/9)/60=60/9=6 6/9=6 2/3 hours