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

Answer: Option A

Let the length of train be $$l$$ metre
According to the question,
Time = $$\frac{\text{Distance}}{\text{Speed}}$$
⇒ 100 =$$\frac{\text{500 + }l}{\text{Speed}}$$
⇒ Speed = $$\frac{500+l}{100}$$    ..... (i)
Again,
60 = $$\frac{\text{250 + }l}{\text{Speed of Train}}$$
Speed = $$\frac{\text{250 + }l}{\text{60}}$$    ..... (ii)
Equation (i) and (ii)
$$\begin{array}{rl}& \Rightarrow \frac{500+l}{100}=\frac{250}{60}\\ & \Rightarrow 1500+3l=1250+5l\\ & \Rightarrow 2l=250\\ & \therefore \text{Length of train = 125 metres}\end{array}$$