in the way of tests

don't you just hate it when a u are studying for a test and it takes u like 2 damn hours to figure out that the prof. just pulled a number out of his ass and forgot to mention it in class?? And when u ask him and he very simply replies “oh yeah I just guessed at that number. Take it for what it’s worth”… What the hell does that mean?? What are the criteria for the guess??? All in all I say FOAD …asshole…