A train can completely cross a 1000 meter long bridge in 15 seconds. It can completely cross another 1300 meter long bridge in 19 seconds. What is the length of the train?

Let's assume the length of the train is 'y' meter.

A train can completely cross a 1000 meter long bridge in 15 seconds.

$$\frac{y+1000}{15} = speed\ of\ train$$    Eq.(i)

It can completely cross another 1300 meter long bridge in 19 seconds.

$$\frac{y+1300}{19} = speed\ of\ train$$    Eq.(ii)

So Eq.(i) = Eq.(ii)

$$\frac{y+1000}{15} = \frac{y+1300}{19}$$

19y+19000 = 15y+19500

19y-15y = 19500-19000

4y = 500

Length of the train = 125 meters