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?	Pick:
A) 10
B) 12
C) 8
D) 15
E) 18

Rationale: "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 b"
Answer: B