Fermi-Estimate the number of passengers using Leeds station in a year


Note that this number could be useful to know for various people
(in lectures we talked about suppliers for the various Cafes in the
station, for example).


Step 1: decide how to break the problem up into factors that are easier
to estimate.
(in lecture we found that everyone in class had used Leeds station at
least once last year, so we've seen it in action.)

We broke it up like this
number of days in year (assuming roughly same activity each day)
number of hours in day (...)
number of platforms (not everyone in class liked this choice of factor - see below)
number of trains per hour per platform
number of carriages per train
number of people per carriage 
proportion of those entering or exiting at Leeds.



Step 2: estimate each factor.
days = 365 (general knowledge!) - for Fermi estimate we made it 500
hours = 24 (general knowledge!) - for Fermi estimate we made it 20
platforms = 17 (general knowledge, for some of us in class!)
trains per platform per hour = 3
   combine these two --> Fermi estimate = 50 trains per hour total
   (which then agreed with other people's estimate by a different route)
carriages = 10
people per carriage = 20
proportion entering or exiting at Leeds = .5

Giving 500x20 x 50 x 10 x 20 x .5
= 10000 x 10000 x .5 = 50,000,000

 
Actual answer (from web, for 2018) = 31,000,000

:-)