To have the final result report the number of questions answered correctly, you will need a custom variable that increments by 1 for each correct answer. This variable should then be referenced on the Result slide to display the total number of correct answers.
However, if your goal is to pass learners based on a specific number of points, you can set the passing score to 50% (which means the learner passes even if one question is answered incorrectly) and reference the scored points instead of the score percentage on the Result slide. This approach allows you to achieve a similar outcome without needing a custom variable.