Working alone, pump A can empty a pool in 4 hours. Working alone, pump B can empty the same pool in 2 hours. Working together, how many minutes will it take pump A and pump B to empty the pool?
Choose the correct choice from the following choices:
A) 65
B) 70
C) 75
D) 80
E) 85
Pump A can empty (1/4) of the pool per hour.   Pump B can empty (1/2) of the pool per hour.   Together the pumps can empty 1/4+1/2=3/4 of the pool per hour.   1 pool / (3/4) pool per hour = 4/3 hours = 80 minutes.   The answer is 80.
<result>D</result>
Working alone, pump A can empty a pool in 4 hours. Working alone, pump B can empty the same pool in 2 hours. Working together, how many minutes will it take pump A and pump B to empty the pool?