Binary Subtraction: 11000100 - 00111011

[dogzilla3]

Hello!

First time posting here. I don't usually reach out to the internet for things like this but I'm stumped so I figured why not.

I'm not 100% sure that this is the right place for this question, but it is technically arithmetic haha. I'm taking a Computer Organization class and one of my homework assignments has this question:

Subtract the following signed binary numbers as shown using the two's complement arithmetic.
a)
11000100
-00111011
b) ...

c) ...

Now it is my understanding that there are three ways to represent signed binary numbers. Signed-magnitude, one's complement, and two's complement. Should I assume that given binary numbers in the problem are signed using two's complement or signed-magnitude? Does it make a difference when doing the problem?

What I got so far... I assumed that they are twos complement numbers...
a)
11000100 (-60)
-00111011 (59) Should end up with -1 right...

Step one: find the two's complement of the subtrahend
00111011 = 11000100 + 1 = 11000101

Step two: add to minuend

carry:	1				1
	1	1	0	0	0	1	0	0
+	1	1	0	0	0	1	0	1
Throw away bit (1)	1	0	0	0	1	0	0	1

The answer that I get is 10001001 (-119), this doesn't seem right. Any ideas?

 

[dogzilla3]

OOOOOOOooooooo_{ooooooo Snap... I think I figured it out. Since they state that the numbers are signed that makes 11000100 a negative because of the leading 1. So that makes 00111011 a positive because of the leading 0. So a negative minus a positive is a larger negative number. So I think -119 is correct as opposed to -1. Sounds right to me, so that's what I'm going with. Binary makes me feel dumb.}