Pre-Algebra Demystified

To add or subtract like terms, add or subtract the numerical coefficients and
use the same variables.

EXAMPLE

Add 7yþ3y.

SOLUTION

7yþ3y¼ð 7 þ 3 Þy

¼10y

EXAMPLE

Subtract 8x
5x.

SOLUTION

8x
5x¼ð 8 
 5 Þx

¼3x

Adding or subtracting like terms is often called ‘‘combining like terms.’’

EXAMPLE

Combine like terms: 9xþ7x
3x
2x.

SOLUTION

9xþ7x
3x
2x¼ð 9 þ 7
3
2 Þx:
¼11x
Unlike terms cannot be added or subtracted. When an expression has both
like and unlike terms, it can be simplified by combining all like terms.

EXAMPLE

Combine like terms: 6x
8xþ2y
3yþ5x
4y.

SOLUTION

6x
8xþ2y
3yþ5x
4y¼6x
8xþ5xþ2y
3y
4y

¼ð 6 
 8 þ 5 Þxþð 2 
 3 
 4 Þy

¼3xþð
 5 Þy

¼3x
5y

CHAPTER 7 Expression and Equations 131