If a train is 100 km away how much sooner would you hear the train coming by listening to the rails (iron) as opposed to listening for it standing by the track?

This problem is a comparison of how fast sound travels through different mediums. The speed of sound in iron is 5950 m/s while in air, it is 331 m/s. Given that the train is 100km away, we can use the given values to solve for the missing values:

Listening through air:

100000/331 = 302 seconds

Listening through the rails:

100000/5950 = 16.81 seconds