36 men can complete a piece of work in 18 days. In how many days will 72 men complete the same work ?  Choose the correct choice from the following
A) 24 B) 17 C) 18 D) 9 E) 11

Rationale: "explanation : less men , means more days { indirect proportion } let the number of days be x then , 72 : 36 : : 18 : x x = 9 answer : d ) 9 days"
Answer: D