A walks around a circular field at the rate of one round per hour while B runs around it at the rate of six rounds per hour. They start at same point at 7:30 am. They shall first cross each other at ?

A. 7:15 am

B. 7:30 am

C. 7: 42 am

D. 7:50 am

Correct Answer :

C. 7: 42 am

Relative speed between two = 6-1 = 5 round per hour They will cross when one round will complete with relative speed, which is 1/5 hour = 12 mins. So 7:30 + 12 mins = 7:42