A 270 metres long train running at the speed of 120 kmph crosses another train running in opposite direction at the speed of 80 kmph in 9 seconds. What is the length of the other train?

A. 290 m
B. 250 m
C. 240 m
D. 230 m

Solution:

\[\left. \begin{array} { l } { \text { Relative speed } = ( 120 + 80 ) km / hr } \\ { = ( 200 \times \frac { 5 } { 18 } ) m / sec } \\ { = ( \frac { 500 } { 9 } ) m / sec } \\ { \text { Let the length of the other train be } x \text { metres. } } \\ { \text { Then, } \frac { x + 270 } { 9 } = \frac { 500 } { 9 } } \\ { \Rightarrow x + 270 = 500 } \\ { \Rightarrow x = 230 } \end{array} \right.\]

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