Two trains of length 100 m and 200 m are 200 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? Answers.
A) 21/9 sec  B) 32/3 sec  C) 20/7 sec  D) 32/3 sec  E) 40/7 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 = 200/35 = 40/7 sec.   Answer:40/7 sec
<result>E</result>
Two trains of length 100 m and 200 m are 200 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?