Working together, 7 identical pumps can empty a pool in 6 hours. How many hours will it take 2 pumps to empty the same pool? Choose the correct choice from the following:
A) 25
B) 24
C) 22
D) 23
E) 21
The answer is E   7 pumps take 6 hours. 1 Pump will take 6*7 hours . Hence 2 pumps will take   (6*7)/2= 
<gadget id="calculator">  (6*7)/2</gadget>
<output>21</output>
21 hours
<result>E</result>
Working together, 7 identical pumps can empty a pool in 6 hours. How many hours will it take 2 pumps to empty the same pool?