A train corsses a pole in 12 sec and crosses a boy sitting in another train coming from opposite direction in 4 sec. If speed of another train in 108 km/hr then find the length of first train is?

Solution : 

Distance constant he both cases
So Time and speed ratio inverse
12:4
1:3
3:1
2==108
1==54

Now, Distance = 54*5/18 *12==180m Ans