Three pipes attached to a tank
Three pipes, a, b, & C are attached to a tank. A & b can fill it in 20 & 30 minutes respectively while C can empty it in 15 minutes. If a, b & C are kept open successively for 1 minute each, how soon will the tank be filled?
you can not fill the tank while pipe c is still opened.. a & b is for storage and pipe C is for draining..
The part of tank filled by Pipe A in 1 min = 1/20
The part of tank filled by Pipe B in 1 min = 1/30
The part of tank emptied by Pipe C in 1 min = 1/15
The part of tank filled in 1 min is 1/20 + 1/30 - 1/15 = 1/60
The total time taken to fill the tank is 60 min = 1 hr.