Example taken from http://stackoverflow.com/questions/3668345/calculate-percentage-in-ruby for percentages in ruby

numeric.rb

# Taken from http://stackoverflow.com/questions/3668345/calculate-percentage-in-ruby
class Numeric
  def percent_of(n)
    self.to_f / n.to_f * 100.0
  end
end

1.percent_of 10    # => 10.0  (%)