Question alternating between correct and incorrect

[John Dickson]

Hi,

I have made up an indices question for an assessment a class will be doing soon.

The link to the question is here,

https://numbas.mathcentre.ac.uk/question/114848/indices/

for part a, despite a correct answer being input there are occasions where the input is being marked correct sometimes and incorrect at others for exactly the same input. Can you shed any light as to why this is happening? 

I've attached a video example of it.

Thanks,

John

[Ben Brawn]

No one can access or look at your question except Christian (and maybe others that work with him) unless you share the correct link, but I would assume the problem is with floating-point errors. Here are some general ideas that I would try:

I'd recommend your answer is entered as, e.g. -3/s^(13), rather than just entering the question again. (again, I can't see what you actually entered), you could tighten up the bounds on the powers so you don't get such large powers in the denominator, change checking accuracy to 0.0000001