Pre-Algebra Demystified

EXAMPLE

Evaluate 5(xþ3y) when x¼
5 and y¼3.

SOLUTION

5 ðxþ3yÞ¼ 5 ð
 5 þ 3 ð 3 ÞÞ

¼ 5 ð
 5 þ 9 Þ

¼ 5 ð 4 Þ

¼ 20

PRACTICE

Evaluate each of the following expressions:

1. 17
   x when x¼ 7


2. xþ2y when x¼
   5 and y¼ 8


3. (2xþ5)^2 when x¼ 6


4. 3x
   2yþz when x¼
   3, y¼4, and z¼ 3


5. 5x^2
   2y^2 when x¼3 and y¼ 6

ANSWERS

1. 10


2. 11


3. 289


4. 
   14


5. 
   27

The Distributive Property

An important property that is often used in algebra is called thedistributive

property:

For any numbers a, b, and c, a(bþc)¼abþac.

The distributive property states that when a sum of two numbers or

expressions in parentheses is multiplied by a number outside the parentheses,

the same result will occur if you multiply each number or expression inside

the parentheses by the number outside the parentheses.

EXAMPLE

Multiply 5(2xþ3y).

128 CHAPTER 7 Expression and Equations