A and B walk around a circular track. A and B walk at a speed of 1 rounds per hour and 4 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 8.30 a.m.?
Choose the correct choice
A) 7  B) 9  C) 4  D) 3  E) 8
Relative speed = Speed of 7 + Speed of B (âˆ´ they walk in opposite directions)   = 1 + 4= 
<gadget id="calculator">1 + 4</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 8.30 am = 1.5 hour   Hence they cross each other 7 times before 8.30 am   7nswer : 7
<result>A</result>
A and B walk around a circular track. A and B walk at a speed of 1 rounds per hour and 4 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 8.30 a.m.?