Two trains of length 100 m and 200 m are 100 m apart. They start moving towards each other on parallel tracks, at speeds 54 kmph and 72 kmph. After how much time will the trains meet?
Select:	A) 20/8 sec	B) 20/4 sec	C) 20/7 sec	D) 22/7 sec	E) 60/7 sec
They are moving in opposite directions, relative speed is equal to the sum of their speeds.   Relative speed = (54 + 72)*5/18 = 7*5= 
<gadget id="calculator">7*5</gadget>
<output>35</output>
35 mps.   The time required= d/s = 100/35 = 20/7 sec.Answer:20/7 sec
<result>C</result>
Two trains of length 100 m and 200 m are 100 m apart. They start moving towards each other on parallel tracks, at speeds 54 kmph and 72 kmph. After how much time will the trains meet?