Pre-Algebra Demystified

Addition of Integers

There are two basic rules for adding integers:

Rule 1: To add two integers with like signs (i.e., both integers are positive

or both integers are negative), add the absolute values of the numbers and

give the sum the common sign.

EXAMPLE

Add (þ2)þ(þ4).

SOLUTION
Since both integers are positive, add the absolute values of each, 2þ 4 ¼6;
then give the answer aþsign. Hence, (þ2)þ(þ4)¼þ6.

EXAMPLE
Addð
3 Þþð
2 Þ:

SOLUTION
Since both integers are negative, add the absolute values 3þ 2 ¼5; then give
the answer a
sign. Hence,ð
3 Þþð
2 Þ¼
5. The rule can be demonstrated
by looking at the number lines shown in Fig. 2-3.

In the first example, you start at 0 and move two units to the right, ending
atþ2. Then fromþ2, move 4 units to the right, ending atþ6. Therefore,
(þ2)þ(þ4)¼þ6.
In the second example, start at 0 and move 3 units to the left, ending on

3. Then from
3, move 2 units to the left, ending at
5. Therefore,ð
3 Þþ
ð
2 Þ¼
5.

CHAPTER 2 Integers 21

Fig. 2-3.