NPS calc in Ruby

nps.rb

class NpsCalculator
  
  def nps(scores)
    (promotor_share(scores) - detractor_share(scores)).round
  end

  private

    def promotor_share(scores)
      scores.count {|score| score > 8} / scores.count.to_f * 100
    end

    def detractor_share(scores)
      scores.count {|score| score < 7} / scores.count.to_f * 100
    end
end

# Usage example
# scores = [9,5,10,6,4,5,7,8,8,9,6]
# puts NpsCalculator.new.nps scores