I am trying to make problems that offer partial credit to students. I have attached a file with a problem I made. There are a couple issues that appear:

1. Here is a video https://use.vg/GGy72U going over how the problem I attached works. More details on my issues in the next two items.

2. If the student enters something not defined in context then the entire answer checker doesn't run. I would like to award credit for answers that the student doesn't mess up. For example, the student gets one of the first two formulas correct, but enters the string "blabla" in the third answer box, the answer checker never runs. I would like to still award points for the first 2 correct answers and even for later answers, just skip this bad input in one of the answer blanks. There is the option of splitting things into multiple answer checkers, but then I can't award the partial credit like I do now because I can't access the other student answers without MultiAnswer.

3. I tried to to use contextArbitraryString.pl. However, I get another problem here. It seems I can't use math objects now. For example. I would like to make formulas from the student answers, but this doesn't seem to work based on my testing. If I can't make formulas then the method I used in the problem attached is useless.

I would also like to edit formulas if I can somehow. For example, look at the string of a student answer and remove any commas from numbers, and then make a math object like a real or formula.

I am sorry if this is written down somewhere, but I have spent a lot of time and haven't been able to figure it out.