Blackboard tests are a hot topic at the moment. On the Digital Learning Connect Teams Area we recently received a question from Dr Gabriel Weymouth:

I’m positive this is clearly documented somewhere, but I can’t find it. How do you make BB apply the correct error margins for calculated formula problems. The logical way of doing it (setting a, say, 2% margin) doesn’t work: Gabriel Weymouth: I’m positive this is clearly documented somewhere, but I can’t find…
posted in Digital Learning Connect/General at 18 Oct 2020 15:53

This took some digging to find out, but now I can clear up this issue.

When you create a Calculated Formula question in Blackboard you can set whether the answer set should use decimal places or significant figures:

What is not made clear is that if you set significant figures, then students have to answer with the same number of significant figures. Here is a test. I wrote the same question, both with an answer range allowance of 2%, one where I set the question to use two significant figures, and the other with two decimals.

In the above screenshot, you can see that I answered within 2% for each question. For the question that used significant figures Blackboard marked my answer incorrect even though I was numerically within 2% of the correct answer:

But if I gave the answer within 2% and the same number of significant figures, it would be correct.

## Conclusion

If you use significant figures, Blackboard marks responses as correct when they provide the same number of significant figures in their answer as well as being within the margin you allow.

Going back to Gabriel’s original question:

Gabriel set this question to use two significant figures and allow a 2% margin.

The student answer 0.6264 has four significant figures. Blackboard marked it incorrect because it used four significant figures, not two. This is regardless of whether numerically it is within the 2% threshold. Blackboard support confirms this is functioning as designed.

## Recommendation

When setting the Answer Set options, use Decimals, and not Significant Figures. If you specify significant figures, then students have to give an answer with the same number of significant figures that you specify, but unless you state this in the question text, they will not know that they need to do so.

Should you use Significant Figures or Decimal Places when setting Answer Set options for Calculated Formula questions in Blackboard?