Cumulative Score in Results Slide

I have built a test exam which consists of a title slide, then a slide which displays 14 topics linked to 14 separate scenes. Each scene has a number of multiple choice (different number of questions for each scene/topic). And finally there is a results slide at the end of each scene to calculate and display the users score for that topic. The use can then review the topic, retry the topic, or go back to the slide with the list of topics.

In addition I have created a slide that I want to display the users cumulative score (based on what ever number of topics he/she has completed). For example, if the user achieved a score of 75% for topic #1 and 85% for topic #2, I want the user to be able to go back to the slide that displays all of the topics and click on a button that takes them to a (cumulative) results slide that should be indicating 80% as their running score. It's not working out that way, because the figure that's showing up on the cumulative results slide is something quite different.

Any suggestions? 

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