Two bullet trains of equal lengths take 10 seconds and 12 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?
Choose the correct answer:
A) 11 sec.
B) 15 sec.
C) 12 sec.
D) 17 sec.
E) 19 sec.
Speed of the first bullet train = 120/10 m/sec = 12 m/sec.   Speed of the second bullet train = 120/12 m/sec = 10 m/sec.   Relative speed = (12 + 10)= 
<gadget id="calculator">(12 + 10)</gadget>
<output>22</output>
22 m/sec.   Required time= (120 + 120)/22 sec = 11 sec.   11 sec.
<result>A</result>
Two bullet trains of equal lengths take 10 seconds and 12 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?