# Homework Help: Finding two numbers in 9's complement arithmetic

1. Oct 16, 2011

### brian.L

1. The problem statement, all variables and given/known data
I have already converted the following numbers 15,765 and -8,773 into 9's complement form. Which gave me the result:

9's Complement of 15,765 = 99,999-84,234 = 84,234
9's Complement of -8,773 = 99,999-(-8,773) = 108,772

Now that I converted the following 5 digit numbers into 9's Complement, am starting to have problems dealing with finding the sum of the two numbers in 9's complement arithmetic and then converting it back into decimal form. I'm not sure if it has anything to do with Sign and magnitude, but can't seem to find a way around this problem.

2. Relevant equations
No equations.

3. The attempt at a solution
My solution so far is:
9's Complement of 15,765 = 99,999-84,234 = 84,234
9's Complement of -8,773 = 99,999-(-8,773) = 108,772

Last edited: Oct 16, 2011
2. Oct 16, 2011

### phinds

Why would the 9's complement of +1 be something different than +1 ?

3. Oct 16, 2011

### brian.L

What do mean? I'm not clear of what you are trying to point out.

4. Oct 16, 2011

### phinds

What I'm trying to point out is that the 9's complement of 1 is 1. 9's complement is a method for representing negative numbers as though they were positive numbers NOT a method for messing up positive numbers.

5. Oct 17, 2011

### phinds

Actually, that was a bit brief.

What I really mean is that you seem to misunderstand the both the purpose and the methodology of complementary number systems and I suggest that you read up on them.

WHY would we want to represent a negative number as a positive number ?

HOW do we choose to do it (what's the difference between 9's complement and 10's complement) ?

what are the tradeoffs in implementing a computer with 1's complement vs 2's complement ?

6. Oct 18, 2011

### brian.L

Sorry, for the late reply. I have just completed the question as well as other questions connected to 9's complement. Can't believe I got stuck on such a simple problem. Turns out a little reading on the topic helped out a lot.

7. Oct 18, 2011