In: Advanced Math
On a particularly strange railway line, there is just
one infinitely long track, so overtaking
is impossible. Any time a train catches up to the one in front of
it, they link up to form a
single train moving at the speed of the slower train. At first,
there are three equally spaced
trains, each moving at a different speed. After all the linking
that will happen has happened,
how many trains are there? What would have happened if the three
equally spaced trains
had started in a different order, but each train kept its same
starting speed? On average
(where we are averaging over all possible orderings of the three
trains), how many trains will there be after a long time has
elapsed? What if at the start there are 4 trains (all moving
at different speeds)? Or 5? Or n? (Assume the Earth is flat and
extends infinitely far in all
directions.)