3 pumps, working 8 hours a day, can empty a tank in 2 days. How many hours a day must 4 pumps work to empty the tank in 1 day?
Choose the correct choice from the following choices:
A) 9	B) 10	C) 11	D) 12	E) 13
Let the required number of working hours per day be x.   More pumps, Less working hours per day (Indirect Proportion)   Less days, More working hours per day (Indirect Proportion)   Pumps	4	:	3 :: 8 : x   Days 1	:	2   Therefore, 4 x 1 x x = 3 x 2 x 8   =&gt; x =(3 x 2 x 8) / (4)   x = 12.   Correct answer is 12
<result>D</result>
3 pumps, working 8 hours a day, can empty a tank in 2 days. How many hours a day must 4 pumps work to empty the tank in 1 day?