Question

pipe A can fill a tank in 20 hours while pipe B can alone fill it in 30 hours and pipe C can empty the full tank in 40 hours if the three pipes are opened together how much will be needed to make tank full

Answer 1

Answer: 120/7 hrs

Step-by-step explanation:

A can fill the tank in 20 hrs, A's 1 hr work = 1/20

B can fill the tank in 30 hrs, B's 1 hr work= 1/30

C can empty the tank in 40 hrs, C's 1 hr work = -1/40

All the pipes are opened together

so (A+B+C)'s Work = (1/20) + (1/30) - (1/40)

                               = (6+4-3) / 120

                                = 7/120

So Time taken by all the pipes to fill the tank is = 120/7 hrs

                                                                               = 17 hrs (Approx)