3 pumps, working 8 hours a day, can empty a tank in 2 days. How many hours a day should 4 pumps work in order to empty the tank in 1 day?	Choose the most appropriate option:
A) 10 B) 12 C) 8 D) 15 E) 18
Explanation:   Let the required hours needed be x   More pumps, less hours (Indirect proportion)   More Days, less hours (Indirect proportion)   Hence we can write as   (pumps)3:4   (days) 2:1}: : x : 8   ⇒3×2×8=4×1 × x   ⇒3×2×2= x   ⇒x=12   Answer: Option 12
<result>B</result>
3 pumps, working 8 hours a day, can empty a tank in 2 days. How many hours a day should 4 pumps work in order to empty the tank in 1 day?