Use average discomfort instead of sum

app/services/tables/discomfort_calculator.rb

@@ -8,7 +8,7 @@ module Tables
     end
 
     def calculate
-      table_size_penalty + cohesion_penalty
+      table_size_penalty + 10 * (cohesion_penalty * 1.0 / table.size)
     end
 
     private

spec/services/tables/discomfort_calculator_spec.rb

@@ -10,6 +10,19 @@ module Tables
     let(:work) { create(:group, name: 'work') }
     let(:school) { create(:group, name: 'school') }
 
+    describe '#calculate' do
+      before do
+        allow(calculator).to receive(:table_size_penalty).and_return(2)
+        allow(calculator).to receive(:cohesion_penalty).and_return(3)
+      end
+
+      let(:table) { Table.new(create_list(:guest, 6)) }
+
+      it 'returns the sum of the table size penalty and the average cohesion penalty' do
+        expect(calculator.calculate).to eq(2 + 10 * 3 / 6.0)
+      end
+    end
+
     describe '#table_size_penalty' do
       before do
         table.min_per_table = 5