# Two trains are running in opposite directions with the same speed. If the length of each train is 120 metres and they cross each other in 12 seconds, then the speed of each train (in km/hr) is:

A. 10

B. 18

C. 36

D. 72

**Answer: Option C **

__Solution(By Examveda Team)__

$$\eqalign{
& {\text{Let}}\,{\text{the}}\,{\text{speed}}\,{\text{of}}\,{\text{each}}\,{\text{train}}\,{\text{be}}\,x\,{\text{m/sec}}. \cr
& {\text{Then,}}\,{\text{relative}}\,{\text{speed}}\,{\text{of}}\,{\text{the}}\,{\text{two}}\,{\text{trains}} = 2x\,{\text{m/sec}} \cr
& {\text{So}},\,2x = \frac{{ {120 + 120} }}{{12}} \cr
& \Rightarrow 2x = 20 \cr
& \Rightarrow x = 10 \cr
& \therefore {\text{Speed}}\,{\text{of}}\,{\text{each}}\,{\text{train}} = 10\,{\text{m/sec}} \cr
& = {10 \times \frac{{18}}{5}} \,{\text{km/hr}} \cr
& = 36\,{\text{km/hr}} \cr} $$ ## Join The Discussion

## Comments ( 1 )

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Two trains are moving in opposite direction with the speed of 36 k.m./h and 54 k.m./h cross each other in 12 seconds. The length of 2nd train is half of the 1st train. 1st train crosses a platform in 1.30 minutes . Than what is the length of platform.