A and B walk around a circular track. A and B walk at a speed of 2 rounds per hour and 3 rounds per hour respectively. If they start at 7 a.m. from the same point in opposite directions, how many times shall they cross each other before 9.30 a.m.?  Select.
A) 10 B) 7 C) 9 D) 5 E) 12
Relative speed = Speed of A + Speed of B (âˆ´ they walk in opposite directions)   = 2 + 3= 
<gadget id="calculator">2 + 3</gadget>
<output>5</output>
5 rounds per hour=&gt; They cross each other 5 times in 1 hour and 2 times in 1/2 hour   Time duration from 7 am to 9.30 am = 2.5 hour   Hence they cross each other 12 times before 9.30 am   Answer : 12
<result>E</result>
A and B walk around a circular track. A and B walk at a speed of 2 rounds per hour and 3 rounds per hour respectively. If they start at 7 a.m. from the same point in opposite directions, how many times shall they cross each other before 9.30 a.m.?