Pipe A can fill a tank in 36 minutes and Pipe B can empty the tank in 45 minutes.If both the pipes are opened simultaneously, then the time (in hours) to fill the tank to half its capacity is:

2 1.5 1.25 1.75

1.5

A+ = 36 min, B- = 45 min, ⇒ Time required by A + B to fill half the tank = \(\frac{180/2}{5-4}\) = 90 min = 1.5 hours.