Download Introduction to Signed Numbers

Addition with Signed Numbers
There are a few different ways of learning how to add signed numbers. Pick the one that
is most suited towards your learning style or try to learn more than one so you will have a
backup method in case your mind goes blank.
1. Bank Accounts. Think of positive numbers as a deposit and negative numbers as
withdrawal. When we add 2 numbers like 14  (8) its like adding a deposit of $14 and a
withdrawal of $8. That would leave us with a positive $6 in our bank account. So
14  (8)  6 or just 6 . What about 11   18 ? That is like depositing $11 but then
withdrawing $18. That would leave us in debt by $7. So 11   18  7 . And what about
something like  6   4 ? That is like withdrawing $6 then withdrawing $4 more. That is like
withdrawing a total of $10. So  6   4  10 . (Hard to withdraw something from nothing?
Just assume you don’t know your balance and just want to know the change in your account.)
2. Number Lines. To use the number line to add, you will plot the first addend on a
number line. Then move on the number line according to the second number. A positive number
would move to the right, while a negative number would move to the left.
+5
Example:  2  5  3
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
-2
Example:  4  2  6
-6
-5
-4
-3
-2
-1
0
1
2
3
4
5
6
3. Memorized Rules. Many students prefer to memorize rules. Just remember,
memorizing rules without an understanding of why they work is a lot harder to retain.
The rules are broken up into two categories:
Adding numbers with the same sign
Step 1 – Add the numbers ignoring sign
Step 2 – Keep the sign
Examples:
Adding numbers with the different signs
Step 1 – Subtract the numbers ignoring sign
Step 2 – Keep the sign of the “larger” number
 2   6  8
11  4  15
 9  8  1
11   4  7
Now you try:
 2  9  ____
 4   8  ____
12   3  ____
15  2  ____
0   7  ____
 10  3  ____
Answers:
7,
17,
-12,
-7,
9
-7