I created a formula question with three variables. It's in the question bank, and I have it in a quiz also. I decided to change the question to have only two variables, and even though I delete the [a], it is not taking that variable away from the variable definition area, so will not allow me to update the question. It has happened a few times before, and the only fix I could find was to recreate the question in a totally new question. I tried updating in both the bank and in the question on the quiz with no luck. Anyone have this happen, and if so, know the problem and a fix?
Is this in the Classic Quiz tool (as opposed to the New Quiz tool)? If so I've observed that I can't add nor delete any variables in questions that I have duplicated from an original (via copying to another bank and copying back). I believe my workaround is similar to the one you stated: 1) create a new question and 2) copy/paste over the text plus rewrite the equations. I've yet to test the New Quiz tool formula questions.
Got it. I should have made it clearer, but my response was targeted @ Classic Quizzes.
In short, I'm having the same issues but have also heard that Canvas is not putting additional efforts into Classic Quizzes as everything is pouring into New Quizzes.