The length of a bridge which a 130 metres long train travelling at 45 Km/hr can cross in 30 seconds is __________

245 m

The speed of the train is given in km/hr, but the time is in seconds and the length is in metres. Let's convert the speed:

$\text{Speed} = 45 \times \frac{5}{18} = 12.5 \text{ m/s}$

The total distance covered by a train while crossing a bridge is equal to the length of the train plus the length of the bridge.

$\text{Total Distance} = \text{Speed} \times \text{Time}$

$\text{Total Distance} = 12.5 \text{ m/s} \times 30 \text{ seconds} = 375 \text{ metres}$

$\text{Total Distance} = \text{Length of Train} + \text{Length of Bridge}$

$375 = 130 + \text{Length of Bridge}$

$\text{Length of Bridge} = 375 - 130 = 245 \text{ metres}$