I'm studying conditional forms, and as I understood most of the time the if clause did not happen, for example in If I had prepared for the interview, I wouldn't be so nervous, so it means that I did not prepare for the interview.
In Summit 2 book there is a note as:
To express inference in conditional sentences, different combinations of tenses can be used:
If you don't know the answer to this question, you didn't do your homework.
My problem is in the meaning, does it mean that you know the answer or not, or it is unknown? Why?