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 5 rounds per hour and 5 rounds per hour respectively. How many times shall they cross each other before 9.30 a.m. ?  Choose one:	A) A)5	B) B)6	C) C)8	D) D)15	E) E)9
Relative speed = 5 + 5= 
<gadget id="calculator">5 + 5</gadget>
<output>10</output>
10 rounds per hour.   So, they cross each other 10 times in an hour and 5 times in half an hour.   Hence, they cross each other 15 times before 9.30 a.m.   ANSWER:15
<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 5 rounds per hour and 5 rounds per hour respectively. How many times shall they cross each other before 9.30 a.m. ?