Pre-Algebra Demystified

Addition and Subtraction

In algebra, theþsign is usually not written when an integer is positive. For

example:

ðþ 8 Þþðþ 2 Þ is written as 8 þ 2

ð
 5 Þ
ðþ 6 Þ is written as 
 5 
 6

ðþ 3 Þ
ðþ 8 Þ is written as 3 
 8

When performing the operations of addition and subtraction in the same

problem, follow these steps:

 Step 1 Write all the positive signs in front of the positive numbers.

 Step 2 Change all the subtractions to addition (remember to add the

opposite).

 Step 3 Add left to right.

EXAMPLE

Perform the indicated operations:

3 þð
 7 Þ
ð
 2 Þþ 5 
 12 þ 8 
ð
 6 Þ

SOLUTION

Step 1: þ 3 þð
 7 Þ
ð
 2 Þþðþ 5 Þ
ðþ 12 Þþðþ 8 Þ
ð
 6 Þ

Step 2: ðþ 3 Þþð
 7 Þþðþ 2 Þþðþ 5 Þþð
 12 Þþðþ 8 Þþðþ 6 Þ

Step 3: ðþ 3 Þþð
 7 Þþðþ 2 Þþðþ 5 Þþð
 12 Þþðþ 8 Þþðþ 6 Þ

¼
 4 þðþ 2 Þþðþ 5 Þþð
 12 Þþðþ 8 Þþðþ 6 Þ

¼
 2 þðþ 5 Þþð
 12 Þþðþ 8 Þþðþ 6 Þ

¼þ 3 þð
 12 Þþðþ 8 Þþðþ 6 Þ

¼
 9 þðþ 8 Þþðþ 6 Þ

¼
 1 þðþ 6 Þ

¼ 5

Hence, the answer is 5.

PRACTICE

For each of the following, perform the indicated operations:

1. 
   6 þ 5
   ð
   9 Þ


2. 12
   ð
   5 Þ
   3


3. 
   18 þ 4
   ð
   7 Þþ 2


4. 3þð
   4 Þ
   ð
   6 Þ


5. 
   5 þ 8
   6 þ 4
   2
   3

26 CHAPTER 2 Integers