A train passes two bridges of lengths 500m and 250m in 100 seconds and 60 seconds respectively. The length of the train is:

Let length of train = $$l$$ m and speed = $$x$$ m/s

Time taken to pass the first bridge (length = 500 m) = $$100=\frac{l+500}{x}$$

=> $$l+500=100x$$ ---------------(i)

Similarly, $$60=\frac{l+250}{x}$$

=> $$l+250=60x$$ ---------------(ii)

Dividing equation (i) by (ii), we get :

=> $$\frac{l+500}{l+250}=\frac{100x}{60x}$$

=> $$\frac{l+500}{l+250}=\frac{5}{3}$$

=> $$3l+1500+5l+1250$$

=> $$5l-3l=1500-1250$$

=> $$2l=250$$

=> $$l=\frac{250}{2}=125$$ m

=> Ans - (B)