Three friends A, B and C run around a circular track of length 120 metres at speeds of 5 m/s, 7 m/sec and 15 m/sec, starting simultaneously from the same point and in the same direction. How often will the three of them meet ?  Choose the correct option.
A) Every 60 seconds
B) Every 120 seconds
C) Every 30 seconds
D) None of these
E) Cannot be determined
Explanation :   A and B will meet for the first time in:   =&gt;(Circumference of track/relative speed) seconds   =&gt;120/2= 
<gadget id="calculator">120/2</gadget>
<output>60</output>
60 seconds.   This also means that A and B will continue meeting each other every 60 seconds.   When B and C will meet for the first time.   B and C will meet for the first time in  120/8= 
<gadget id="calculator"> 120/8</gadget>
<output>15</output>
15 seconds.   This also means that they will meet every 15 seconds after they meet for the first time i.e. A and B meet every 60 seconds and multiples of 60 seconds and B and C meet every 15 seconds and multiples of 15 seconds.   The common multiples to both these time, will be when A and B and B and C will meet i.e. when A, B and C will meet.   The common multiple of 60 and 15 will be 60,120,180 etc. i.e. they will meet every 60 seconds.   Every 60 secondsnswer : Every 60 seconds
<result>A</result>
Three friends A, B and C run around a circular track of length 120 metres at speeds of 5 m/s, 7 m/sec and 15 m/sec, starting simultaneously from the same point and in the same direction. How often will the three of them meet ?