How to Use Average score in questions to have a display logic for another question.

Hi All,
How to Use Average score in questions to have a display logic for another question.
Example:
Scale rating 0-10
Question 1: How do you rate your Car performance.
Question 2: How do you rate your motorcycle performance.
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Now, I want to use the score of Q#1 and Q#2 to have an average greater than 5 and this condition should be the display logic for my question 3.
Any idea on how to do this?