diff --git a/app/controllers/exercises_controller.rb b/app/controllers/exercises_controller.rb
index 72b5ce2f..839aef4c 100644
--- a/app/controllers/exercises_controller.rb
+++ b/app/controllers/exercises_controller.rb
@@ -187,28 +187,8 @@ class ExercisesController < ApplicationController
     count_interventions_today = UserExerciseIntervention.where(user: current_user).where("created_at >= ?", Time.zone.now.beginning_of_day).count
     user_got_intervention_in_exercise = UserExerciseIntervention.where(user: current_user, exercise: @exercise).size >= max_intervention_count_per_exercise
     user_got_enough_interventions = count_interventions_today >= max_intervention_count_per_day or user_got_intervention_in_exercise
-    @is_experimental_course = @course_token and experimental_course?(@course_token)
-
-    @experiment_group = UserGroupSeparator.getInterventionGroup(current_user)
-
-    showInterventions = (@is_experimental_course and not user_solved_exercise and not user_got_enough_interventions) ? "true" : "false"
-
-    case @experiment_group
-      when :rfc_intervention_stale_rfc
-        @show_rfc_interventions = showInterventions
-      when :break_intervention_stale_rfc
-        @show_break_interventions = showInterventions
-      when :no_intervention_stale_rfc
-      when :no_intervention_hide_rfc
-        @hide_rfc_button = "true"
-      when :break_intervention_show_rfc
-        @show_break_interventions = showInterventions
-      when :no_intervention_show_rfc
-      when :rfc_intervention_show_rfc
-        @show_rfc_interventions = showInterventions
-    end
-
 
+    @show_rfc_interventions = (not user_solved_exercise and not user_got_enough_interventions).to_s
 
 
     @search = Search.new
@@ -430,11 +410,6 @@ class ExercisesController < ApplicationController
           return
         end
 
-        if @is_experimental_course and (@rfc_group == :hide_rfc)
-          redirect_to_lti_return_path
-          return
-        end
-
         rfc = @submission.own_unsolved_rfc
         if rfc
           # set a message that informs the user that his own RFC should be closed.
diff --git a/app/helpers/request_for_comments_helper.rb b/app/helpers/request_for_comments_helper.rb
deleted file mode 100644
index f46a73e4..00000000
--- a/app/helpers/request_for_comments_helper.rb
+++ /dev/null
@@ -1,2 +0,0 @@
-module RequestForCommentsHelper
-end
diff --git a/app/models/proxy_exercise.rb b/app/models/proxy_exercise.rb
index de997a0e..328fffa6 100644
--- a/app/models/proxy_exercise.rb
+++ b/app/models/proxy_exercise.rb
@@ -36,31 +36,15 @@ class ProxyExercise < ApplicationRecord
           Rails.logger.debug("retrieved assigned exercise for user #{user.id}: Exercise #{assigned_user_proxy_exercise.exercise}" )
           assigned_user_proxy_exercise.exercise
         else
+          Rails.logger.debug("find new matching exercise for user #{user.id}" )
           matching_exercise =
-              if (token.eql? "e85689d5")
-                Rails.logger.debug("Proxy exercise with token e85689d5, split user in groups..")
-                group = UserGroupSeparator.getGroupExerciseDescriptionTesting(user)
-                Rails.logger.debug("user assigned to group #{group}")
-                case group
-                  when :group_a
-                    exercises.where(id: 557).first
-                  when :group_b
-                    exercises.where(id: 558).first
-                  when :group_c
-                    exercises.where(id: 559).first
-                  when :group_d
-                    exercises.where(id: 560).first
-                end
-              else
-                Rails.logger.debug("find new matching exercise for user #{user.id}" )
-                begin
-                  find_matching_exercise(user)
-                rescue => e #fallback
-                  Rails.logger.error("finding matching exercise failed. Fall back to random exercise! Error: #{$!}" )
-                  @reason[:reason] = "fallback because of error"
-                  @reason[:error] = "#{$!}:\n\t#{e.backtrace.join("\n\t")}"
-                  exercises.where("expected_difficulty > 1").shuffle.first # difficulty should be > 1 to prevent dummy exercise from being chosen.
-                end
+              begin
+                find_matching_exercise(user)
+              rescue => e #fallback
+                Rails.logger.error("finding matching exercise failed. Fall back to random exercise! Error: #{$!}" )
+                @reason[:reason] = "fallback because of error"
+                @reason[:error] = "#{$!}:\n\t#{e.backtrace.join("\n\t")}"
+                exercises.where("expected_difficulty > 1").shuffle.first # difficulty should be > 1 to prevent dummy exercise from being chosen.
               end
           user.user_proxy_exercise_exercises << UserProxyExerciseExercise.create(user: user, exercise: matching_exercise, proxy_exercise: self, reason: @reason.to_json)
           matching_exercise
@@ -69,42 +53,27 @@ class ProxyExercise < ApplicationRecord
     end
 
     def find_matching_exercise(user)
-      user_group = UserGroupSeparator.getProxyExerciseGroup(user)
-      case user_group
-        when :dummy_assigment
-          rec_ex = select_easiest_exercise(exercises)
-          @reason[:reason] = "dummy group"
-          Rails.logger.debug("assigned user to dummy group, and gave him exercise: #{rec_ex.title}")
-          rec_ex
-        when :random_assigment
-          @reason[:reason] = "random group"
-          ex = exercises.where("expected_difficulty > 1").shuffle.first
-          Rails.logger.debug("assigned user to random group, and gave him exercise: #{ex.title}")
-          ex
-        when :recommended_assignment
-          exercises_user_has_accessed = user.submissions.where("cause IN ('submit','assess')").map{|s| s.exercise}.uniq.compact
-          tags_user_has_seen = exercises_user_has_accessed.map{|ex| ex.tags}.uniq.flatten
-          Rails.logger.debug("exercises_user_has_accessed #{exercises_user_has_accessed.map{|e|e.id}.join(",")}")
+        exercises_user_has_accessed = user.submissions.where("cause IN ('submit','assess')").map{|s| s.exercise}.uniq.compact
+        tags_user_has_seen = exercises_user_has_accessed.map{|ex| ex.tags}.uniq.flatten
+        Rails.logger.debug("exercises_user_has_accessed #{exercises_user_has_accessed.map{|e|e.id}.join(",")}")
 
-          # find exercises
-          potential_recommended_exercises = []
-          exercises.where("expected_difficulty >= 1").each do |ex|
-            ## find exercises which have only tags the user has already seen
-            if (ex.tags - tags_user_has_seen).empty?
-              potential_recommended_exercises << ex
-            end
+        # find exercises
+        potential_recommended_exercises = []
+        exercises.where("expected_difficulty >= 1").each do |ex|
+          ## find exercises which have only tags the user has already seen
+          if (ex.tags - tags_user_has_seen).empty?
+            potential_recommended_exercises << ex
           end
-          Rails.logger.debug("potential_recommended_exercises: #{potential_recommended_exercises.map{|e|e.id}}")
-          # if all exercises contain tags which the user has never seen, recommend easiest exercise
-          if potential_recommended_exercises.empty?
-            Rails.logger.debug("matched easiest exercise in pool")
-            @reason[:reason] = "easiest exercise in pool. empty potential exercises"
-            select_easiest_exercise(exercises)
-          else
-            select_best_matching_exercise(user, exercises_user_has_accessed, potential_recommended_exercises)
-          end
-      end
-
+        end
+        Rails.logger.debug("potential_recommended_exercises: #{potential_recommended_exercises.map{|e|e.id}}")
+        # if all exercises contain tags which the user has never seen, recommend easiest exercise
+        if potential_recommended_exercises.empty?
+          Rails.logger.debug("matched easiest exercise in pool")
+          @reason[:reason] = "easiest exercise in pool. empty potential exercises"
+          select_easiest_exercise(exercises)
+        else
+          select_best_matching_exercise(user, exercises_user_has_accessed, potential_recommended_exercises)
+        end
     end
     private :find_matching_exercise
 
diff --git a/app/models/submission.rb b/app/models/submission.rb
index 13eb6ff2..e9d3b235 100644
--- a/app/models/submission.rb
+++ b/app/models/submission.rb
@@ -66,10 +66,6 @@ class Submission < ApplicationRecord
   end
 
   def unsolved_rfc
-    # old query
-    # RequestForComment.unsolved.where(exercise_id: exercise).where.not(question: nil).order("RANDOM()").find { | rfc_element |(rfc_element.comments_count < MAX_COMMENTS_ON_RECOMMENDED_RFC) }
-
-    # experimental query:
-    RequestForComment.unsolved.joins('JOIN exercise_collection_items eci ON eci.exercise_id = request_for_comments.exercise_id').where('eci.exercise_collection_id != 3 OR user_id%10 > 3').where(exercise_id: exercise).where.not(question: nil).order("RANDOM()").find { | rfc_element |(rfc_element.comments_count < MAX_COMMENTS_ON_RECOMMENDED_RFC) }
+    RequestForComment.unsolved.where(exercise_id: exercise).where.not(question: nil).order("RANDOM()").find { | rfc_element |( (rfc_element.comments_count < MAX_COMMENTS_ON_RECOMMENDED_RFC) && (!rfc_element.question.empty?)) }
   end
 end
diff --git a/app/views/request_for_comments/index.html.slim b/app/views/request_for_comments/index.html.slim
index eb222e31..94262267 100644
--- a/app/views/request_for_comments/index.html.slim
+++ b/app/views/request_for_comments/index.html.slim
@@ -23,8 +23,7 @@ h1 = RequestForComment.model_name.human(count: 2)
         th = t('activerecord.attributes.request_for_comments.last_update')
     tbody
       - @request_for_comments.each do |request_for_comment|
-        - do_not_answer = [:rfc_intervention_stale_rfc, :break_intervention_stale_rfc, :no_intervention_stale_rfc].include?(UserGroupSeparator.getInterventionGroup(request_for_comment.user)) and current_user.internal_user?
-        tr data-id=request_for_comment.id class=('do-not-answer' if do_not_answer)
+        tr data-id=request_for_comment.id
           - if request_for_comment.solved?
             td
               span class="fa fa-check" aria-hidden="true"
diff --git a/lib/user_group_separator.rb b/lib/user_group_separator.rb
deleted file mode 100644
index 2333b686..00000000
--- a/lib/user_group_separator.rb
+++ /dev/null
@@ -1,48 +0,0 @@
-class UserGroupSeparator
-
-  # seperates user into 20% no intervention, 20% break intervention, 60% rfc intervention
-  def self.getInterventionGroup(user)
-    lastDigitId = user.id % 10
-    if lastDigitId < 1 # 0
-      :rfc_intervention_stale_rfc
-    elsif lastDigitId < 2 # 1
-      :break_intervention_stale_rfc
-    elsif lastDigitId < 3 # 2
-      :no_intervention_stale_rfc
-    elsif lastDigitId < 4 # 3
-      :no_intervention_hide_rfc
-    elsif lastDigitId < 5 # 4
-      :break_intervention_show_rfc
-    elsif lastDigitId < 6 # 5
-      :no_intervention_show_rfc
-    else # 6,7,8,9
-      :rfc_intervention_show_rfc
-    end
-  end
-
-  # seperates user into 20% dummy assignment, 20% random assignemnt, 60% recommended assignment
-  def self.getProxyExerciseGroup(user)
-    lastDigitCreatedAt = user.created_at.to_i % 10
-    if lastDigitCreatedAt < 2 # 0,1
-      :dummy_assigment
-    elsif lastDigitCreatedAt < 4 # 2,3
-      :random_assigment
-    else # 4,5,6,7,8,9
-      :recommended_assignment
-    end
-  end
-
-  def self.getGroupExerciseDescriptionTesting(user)
-    groupById = user.id % 4
-    if groupById == 0
-      :group_a
-    elsif groupById == 1
-      :group_b
-    elsif groupById == 2
-      :group_c
-    else # 3
-      :group_d
-    end
-  end
-
-end
\ No newline at end of file