3 bodies x , y and z start moving around a circular track of length 960 m from the same point simultaneously in the same direction at speeds of 12 m / s , 20 m / s and 36 m / s respectively . when will they meet for the first time after they started moving ?  Choose the correct choice from the following answers.
A) 240 seconds  B) 120 seconds  C) 60 seconds  D) 180 seconds  E) 100 seconds

Rationale: if they all meet after t seconds , it means they covered the distances 12 t , 20 t , and 36 t respectively . since they all arrive to the same spot , it means that the differences taken pairwise between the distances must be positive integer multiples of the length of the track , which is 960 m . so , 8 t , 16 t , and 24 t must all be multiples of 960 . 8 t multiple of 960 means t multiple of 120 . the smallest t with this property is 120 and is on the list of answers . answer b .
Answer: B