A and B walk around a circular track. They start at 8 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 9.30 a.m. ? Choose one.
A) 5	B) 6	C) 8	D) 7	E) 9
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 2 times in half an hour.   Hence, they cross each other 7 times before 9.30 a.m.   ANSWER:7
<result>D</result>
A and B walk around a circular track. They start at 8 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 9.30 a.m. ?