A moving train passes a platform 50 m long in 14 seconds and a lamp post in 10 seconds. The speed of the train (in km/hr) is :

Answer: Option D

Let length of train be x and speed be S
S = $$\frac{x+50}{14}$$ , also S = $$\frac{x}{10}$$
Then,
$$\frac{x+50}{14}$$ = $$\frac{x}{10}$$
5x + 250 = 7x
2x = 250
x = 125
∴ Speed :
= $$\frac{125}{10}$$ × $$\frac{18}{5}$$
= 45 km/hr