Change result based on number of questions answered

Hi,

I have a slide that asks the user how many questions they want to have in a quiz (for helping them distinguish vowel sounds).

They have the choice of 10, 20 or 30. Depending on the answer, they will be branched to either the slides with the respective number of question slides.

However when I choose something like 10, it gives me a really low score even if I get all 10 questions right because it's taking into account the possible questions in other branches.

How can I fix my formula to only take into account the questions I've answered?

thanks