def disease_spread(rate, population, days)
  newly_sick = 1
  total_sick = 1
  print "time", "\t", "new", "\t", "total", "\t", "ratio", "\t\n" 
  for time in 1 .. days do 
    print time, "\t"
    newly_sick = newly_sick * rate
    print newly_sick, "\t"
    total_sick = total_sick + newly_sick
    print total_sick, "\t"
    ratio = 1.0 * total_sick / population
    print ratio, "\n"  
  end
  return ratio
end