Let the length of the first train be ' x ' meters and its speed be ' y ' km/h. Now, (x+250)=y×36×5∕18=10y (x+150)=(y+40)×18×5∕18=5(y+40) From (1) and (2): 10y=5(y+40)+100 ⇒y=60km∕h ⇒x=350m Let the time taken by first train to cross pole be ' t ' seconds ⇒350=60×t×