Question

pipe a can fill an empty tank in 5 hours while pipe b can empty the full tank in 6 hours . if both are opened at the same time in the empty tank, how much time will they take to fill it up completely ?

Answer 1

Pipe A can fill the tank in 5 hrs, So A's 1 hr Work = 1/5

Pipe B can empty a full tank in 6 hrs, So B's 1 hr Work  = -1/6

Now both the pipes are opened

(A+B)'s work = (1/5) + (-1/6)

                     = 1/30

So Both the pipe will take 30 Hours to fill up the tank completely