Two tains of equal lengths take 10 seconds and 12 seconds respectively to cross a telegraph post. If the length of each train be 120 metres, in what time (in seconds) will they cross each other travelling in opposite direction?  Answers:
A) 12 B) 14 C) 10.9 D) 20 E) 18
Sol.   Speed of the first train = [120 / 10] m/sec = 12 m/sec.   Speed of the second train = [120 / 12] m/sec = 10 m/sec.   Relative speed = (12 + 10) = m/sec = 22 m/sec.   ∴ Required time = (120 + 120) / 22 secc = 10.9 sec.   Answer 10.9
<result>C</result>
Two tains of equal lengths take 10 seconds and 12 seconds respectively to cross a telegraph post. If the length of each train be 120 metres, in what time (in seconds) will they cross each other travelling in opposite direction?