gistfile1

#!/usr/bin/env ruby -rrubygems

require 'activesupport'
require 'ostruct'

bprb = [
  {:date => Date.new(2008,  9, 17), :attendees => 52},
  {:date => Date.new(2008, 10, 16), :attendees => 30},
  {:date => Date.new(2008, 11, 20), :attendees => 25},
  {:date => Date.new(2008, 12, 17), :attendees => 8},
  {:date => Date.new(2009,  1, 22), :attendees => 20},
  {:date => Date.new(2009,  2, 24), :attendees => 23},
  {:date => Date.new(2009,  4, 23), :attendees => 20},
  {:date => Date.new(2009,  5, 28), :attendees => 30},
  {:date => Date.new(2009,  6, 18), :attendees => 9},
  {:date => Date.new(2009,  7, 16), :attendees => 12},
  {:date => Date.new(2009,  8, 27), :attendees => 14},
  {:date => Date.new(2009,  9, 17), :attendees => 42},
].map! {|m| OpenStruct.new(m)}

bp = OpenStruct.new(
  :pop => 1_712_210,
  :area => 525.16,
  :lat => 47.471944,
  :lng => 19.050278
)

a = bprb.inject(0) {|a,m| a+m.attendees} / bprb.size.to_f
b = Math.sqrt(bp.pop / bp.area)
c = Math.sqrt(bp.lat * bp.lng)

((a+2*b+c)/4).to_i # => 42