Two trains 140 m and 200 m long run at the speed of 60 km/hr and 40 km/hr respectively in opposite directions on parallel tracks. The time which they take to cross each other is?
Pick one:  A) 10.9 sec  B) 8.64 sec  C) 53.8 sec  D) 10.8 sec  E) 10.4 sec
Relative speed = 60 + 40= 
<gadget id="calculator">60 + 40</gadget>
<output>100</output>
100 km/hr.= 100 * 5/18 = 250/9 m/sec.   Distance covered in crossing each other = 140 + 200 = 240 m.   Required time = 240 * 9/250= 
<gadget id="calculator">240 * 9/250</gadget>
<output>216/25 = around 8.64</output>
8.64 sec.   Answer: 8.64 sec:
<result>B</result>
Two trains 140 m and 200 m long run at the speed of 60 km/hr and 40 km/hr respectively in opposite directions on parallel tracks. The time which they take to cross each other is?