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 4 rounds per hour and 4 rounds per hour respectively. How many times shall they cross each other before 9.30 a.m. ?
Choose the correct answer: A) A)5 B) B)6 C) C)8 D) D)12 E) E)9
Relative speed = 4 + 4= 
<gadget id="calculator">4 + 4</gadget>
<output>8</output>
8 rounds per hour.   So, they cross each other 8 times in an hour and 4 times in half an hour.   Hence, they cross each other 12 times before 9.30 a.m.   ANSWER:12
<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 4 rounds per hour and 4 rounds per hour respectively. How many times shall they cross each other before 9.30 a.m. ?