How to add an N/A option to a numeric question?
e.g. most entries will be numeric answers between 1 and 100
sometimes the answer could be NA or N/A i.e. Not Applicable.
I think the best option might be to use a regular Textbox Question:
You can then use the Auto-Suggest option and populate it with only the acceptable answers: 1-100 & NA:
Make sure the check the Only allow answers from the auto-complete list.
Hope this helps!