Two trains 180 metres and 120 metres in length are running towards each other on parallel tracks, one at the rate 65 km/hr and another at 55 km/hr. In how many seconds will they be cross each other from the moment they meet ?

A. 6 seconds

B. 9 seconds

C. 12 seconds

D. 15 seconds

Answer: Option B

Solution(By Examveda Team)

Time taken by trains to cross each other in opposite direction
$$\frac{{{l_1} + {l_2}}}{{{\text{Relative speed in opposite direction}}}}$$
$$\eqalign{ & {\text{ = }}\frac{{\left( {180 + 120} \right)}}{{\left( {65 + 55} \right)}} \cr & {\text{ = }}\frac{{300}}{{120 \times \frac{5}{{18}}}} \cr & {\text{ = 9 seconds}} \cr} $$