diff --git a/FAQ%3A-JOJ3-usage.md b/FAQ%3A-JOJ3-usage.md
index 8dcb4f7..99976a7 100644
--- a/FAQ%3A-JOJ3-usage.md
+++ b/FAQ%3A-JOJ3-usage.md
@@ -18,6 +18,10 @@ A: While JOJ3 and health check could have bugs, we have not seen any false posit
 
 A: A working program should return with status (or code) 0. If something unexpected is happening JOJ or the OS might be sending a *signal* to your program. To understand what went wrong, run the following command `kill -L`. It lists all the signal names in a table. Check the name of the signal corresponding to the number you see in your Gitea issue and run a quick online search. 
 
+**Q: For test cases I can see some unexpected `+` and `-` that I didn't input in my code. Where are they coming from?**
+
+A: When running test cases two things can happen: (i) you pass, ie. your output matches the expected sample or (ii) you failed, ie. there are differences between your output and the expected sample. Extra lines are marked with `+` while missing ones appear with a `-`. 
+
 **Q: I found a bug, what should I do?**
 
 A: First make sure this is really a bug, then open an issue in course-support to report it. We will come back to you for more details if necessary.