Working alone, pump A can empty a pool in 4 hours. Working alone, pump B can empty the same pool in 6 hours. Working together, how many minutes will it take pump A and pump B to empty the pool?  Options
A) 132 B) 138 C) 144 D) 150 E) 156

Rationale: pump a can empty ( 1 / 4 ) of the pool per hour . pump b can empty ( 1 / 6 ) of the pool per hour . together the pumps can empty 1 / 4 + 1 / 6 = 5 / 12 of the pool per hour . 1 pool / ( 5 / 12 ) pool per hour = 12 / 5 hours = 144 minutes . the answer is c .
Answer: C