A and B walk around a circular track. They start at 9 a.m. from the same point in the opposite directions. A and B walk at a speed of 2 rounds per hour and 3 rounds per hour respectively. How many times shall they cross each other before 10:00 a.m.?
Choose the most appropriate option:
A) 8  B) 7  C) 6  D) 5  E) 10

Rationale: sol . relative speed = ( 2 + 3 ) = 5 rounds per hour . so , they cross each other 5 times in an hour and 5 times in next hour . hence , they cross each other 10 times before 10 : 00 a . m . answer e
Answer: E