Two trains of length 100 m and 200 m are 100 m apart. They start moving towards each other on parallel tracks, at speeds 90 kmph and 72 kmph. After how much time will the trains meet?
Choose the correct choice from the following options.
A) 27/7 sec B) 20/9 sec C) 33/7 sec D) 21/7 sec E) 32/7 sec
They are moving in opposite directions, relative speed is equal to the sum of their speeds.   Relative speed = (90 + 72)*5/18 = 9*5= 
<gadget id="calculator">9*5</gadget>
<output>45</output>
45 mps.   The time required= d/s = 100/45 = 20/9 sec.   Answer : 20/9 sec
<result>B</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 90 kmph and 72 kmph. After how much time will the trains meet?