A walks around a circular field at the rate of one round per hour while B runs around it at the rate of five rounds per hour. They start in the same direction from the same point at 7.30 a.m. They shall first cross each other after___ minutes?  Choose the correct choice from the following options:
A) 11 min B) 12 min C) 10 min D) 15 min E) 16 min
Since A and B move in the same direction along the circle, so they will first meet each other when there is a difference of one round between the two.   Relative speed of A and B = 5 - 1= 
<gadget id="calculator">5 - 1</gadget>
<output>4</output>
4 rounds per hour.   Time taken to complete one round at this speed= 1/4 hr = 15 min.   15 min
<result>D</result>
A walks around a circular field at the rate of one round per hour while B runs around it at the rate of five rounds per hour. They start in the same direction from the same point at 7.30 a.m. They shall first cross each other after___ minutes?