Question

Two trains of equal lengths take 10 seconds and 15 seconds respectively to cross a telegraph post. If the length of each train is 120 metres, in what time (in seconds) will they cross each other travelling in opposite direction?

• A. 10
• B. 12
• C. 15
• D. 20
• E. 25

Answer 1

The correct option is B

12

Speed of the first train = $\left(\frac{120}{10}\right)$m/sec = 12 m/sec

Speed of the second train = $\left(\frac{120}{15}\right)$m/sec = 8 m/sec

Relative speed = (12+8) m/sec = 20 m/sec.

$\therefore$Required time = $\frac{\left(120+120\right)}{20}$sec = 12 sec.