Two bullet train s 140 m and 160 m long run at the speed of 60 km/hr and 40 km/hr respectively in opposite directions on parallel tracks. The time (in seconds) which they take to cross each other, is:
Pick.
A) 15.8 sec.  B) 12.8 sec.  C) 11.8 sec.  D) 10.8 sec.  E) 08.8 sec.
D   10.8 sec.   Relative speed = (60 + 40) km/hr = 100x5/18 = 250/9 m/ sec.   Distance covered in crossing each other = (140 + 160)= 
<gadget id="calculator">(140 + 160)</gadget>
<output>300</output>
300 m.   Required time= 300x9/250 = 54/5= 
<gadget id="calculator">54/5</gadget>
<output>54/5 = around 10.8</output>
10.8 sec.
<result>D</result>
Two bullet train s 140 m and 160 m long run at the speed of 60 km/hr and 40 km/hr respectively in opposite directions on parallel tracks. The time (in seconds) which they take to cross each other, is: