The document defines numerical expressions, variables, and variable expressions. It provides examples of how to evaluate variable expressions by substituting number values for the variables and evaluating the resulting numerical expression. Four examples are shown with step-by-step solutions for evaluating expressions containing multiple variables when given the values of the variables.

1. Introduction
EXPRESSIONS AND
VARIABLES

2. DEFINITIONS
 A numerical expression consists of
numbers and operations, (e.g. 4×10).
 A variable is a letter used to represent one
or more numbers (e.g.푎, 푏, 푤).
 Variable expression consists of numbers,
variables and operations.

3. EVALUATING VARIABLE EXPRESSION
To evaluate a variable expression, substitute a
number for each variable and evaluate the
resulting numerical expression.

4. EXAMPLE 1
Evaluate the expression 15 − 푥 when 푥 = 6
Solution
15 − 푥 = 15 − 6
= 9

5. EXAMPLE 2
Evaluate the expression 푥푦 + 22 when 푥 =
10 푎푛푑 푦 = 4
Solution
푥푦 + 22 = 10 × 4 + 22 (Substitute the values)
= 40 + 22
= 62

6. EXAMPLE 3
Evaluate the expression
푏
푎
+ 푐 when 푎 = 2, 푏 =
15 푎푛푑 푐 = 3.5
Solution
푏
푎
+ 푐 =
15
2
+ 3.5 (Substitute the
values)
= 7.5 + 3.5
= 11

7. EXAMPLE 4
Evaluate the expression 푥푦 − 푦푧 + 푥 when 푥 = 2, 푦 =
− 1 푎푛푑 푧 = 4?
Solution
푥푦 − 푦푧 + 푥 = 2 −1 − −1 4 + (2) (Substitute the values)
= −2 − −4 + 2 (Multiply)
= −2 + 4 + 2
= 4 (Add)