If 36 men can do a piece of work in 25 hours, in how many hours will 15 men do it ?	Select:  A) 10 hours  B) 40 hours  C) 20 hours  D) 60 hours  E) none of them

Rationale: "let the required number of hours be x . then , less men , more hours ( indirect proportion ) 15 : 36 : : 25 : x = ( 15 x x ) = ( 36 x 25 ) = ( 36 x 25 ) / 15 = 60 hence , 15 men can do it in 60 hours . answer is d ."
Answer: D