Two bullet trains of equal lengths take 10 seconds and 50 seconds respectively to cross a telegraph post. If the length of each bullet train be 120 metres, in what time (in seconds) will they cross each other travelling in opposite direction?	Answers:	A) 13 sec.	B) 15 sec.	C) 12 sec.	D) 17 sec.	E) 16.7 sec.
Speed of the first bullet train = 120/10 m/sec = 12 m/sec.   Speed of the second bullet train = 120/50 m/sec = 2.4 m/sec.   Relative speed = (12 + 2.4)= 
<gadget id="calculator">(12 + 2.4)</gadget>
<output>14.4</output>
14.4 m/sec.   Required time= (120 + 120)/14.4 sec = 16.7 sec.   16.7 sec.
<result>E</result>
Two bullet trains of equal lengths take 10 seconds and 50 seconds respectively to cross a telegraph post. If the length of each bullet train be 120 metres, in what time (in seconds) will they cross each other travelling in opposite direction?