Two trains of length 100 meters and 200 meters are 140 meters apart. They are moving towards each other on parallel tracks, at speeds of 54 km/h and 72 km/h. After how many seconds will the trains meet?
Select
A) 2
B) 4
C) 6
D) 8
E) 10
The speeds are 54000/3600= 
<gadget id="calculator">54000/3600</gadget>
<output>15</output>
15 m/s and 72000/3600= 
<gadget id="calculator">72000/3600</gadget>
<output>20</output>
20 m/s   The relative speed is 35 m/s.   time= 140 / 35= 
<gadget id="calculator">140 / 35</gadget>
<output>4</output>
4 seconds   The answer is 4.
<result>B</result>
Two trains of length 100 meters and 200 meters are 140 meters apart. They are moving towards each other on parallel tracks, at speeds of 54 km/h and 72 km/h. After how many seconds will the trains meet?