A motorcyclist X drives along a circular fence at a rate of 2 rounds per hour and another motor cyclist Y at a rate of 4 rounds per hour. After how long they will cross each other for the first time?  Options:
A) 10 min
B) 20 min
C) 30 min
D) 40 min
E) none of these

Rationale: explanation : since x and y move in the same direction they cross each other when there is a difference of two round between the two . relative speed of x and y = 4 - 2 = 2 . time taken to complete one round at this speed = 1 / 2 hour = 30 minutes answer : c
Answer: C