number systems/signing

Hi /prog/

How does one represent negative numbers in hex/octal, e.g -15. Would the hex value be F1 or -0F? In the example i've been given it says -15 is F1, but I dont see how the sign is represented, shouldn't F1 be +241?

>>10
I'm not the one making the uneducated comments. Now go run along you hourly worker you. BTW, I'm still not granting your stupid ass the first technical interview.