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 correct choice from the following
A) 8  B) 7  C) 6  D) 5  E) 10
Sol.   Relative speed = (2 + 3)= 
<gadget id="calculator">(2 + 3)</gadget>
<output>5</output>
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 10
<result>E</result>
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.?