Use sum instead of map + inject

app/models/conversational_development_index/idea_to_production_step.rb

@@ -9,9 +9,9 @@ module ConversationalDevelopmentIndex
     end
 
     def percentage_score
-      sum = features.map do |feature|
+      sum = features.sum do |feature|
         metric.percentage_score(feature)
-      end.inject(:+)
+      end
 
       sum / features.size.to_f
     end

app/presenters/conversational_development_index/metric_presenter.rb

@@ -138,7 +138,7 @@ module ConversationalDevelopmentIndex
     end
 
     def average_percentage_score
-      cards.map(&:percentage_score).inject(:+) / cards.size.to_f
+      cards.sum(&:percentage_score) / cards.size.to_f
     end
   end
 end