Problem: 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 20 minutes. if a, b & c are kept open successively for 1.5 minute each, how soon will the tank be filled ?
Options: a. 2 hours, b. 4 hours, c. 5 hours, d. 2 hours 15 min, e. 3 hours
d