1. This lesson teaches students how to substitute numbers for letters in algebraic expressions. 2. A variable is a symbol used for an unknown number. Substitution is the process of replacing variables with given numbers to simplify expressions and find numerical values. 3. Examples show substituting specific values for variables into expressions, then using arithmetic to simplify and find the solution.

1. Lesson 3

2. Objectives
After completion of this lesson, students should be able to:
1. Substitute numbers for letters in Algebraic Expressions

3. Recall the parts of an expression from our last lesson, in this lesson we are going to focus on
variables in the expression. Remember, a variable is a symbol used for an unknown number in an
algebraic expression.
In some cases the number for the variable is given to you and you are required to use the number in
place of the variable and perform calculations to arrive at a solution. This process is known as
substitution.

4. Substitution is the process whereby the symbol(s) in an algebraic expression is replaced by
given number(s) in order to simplify and find its particular numerical value. When substituting a
number for a symbol in an algebraic expression we must pay particular attention so as not
to change the form of the expression. This means that we substitute the number for the
symbol directly into the algebraic expression and thus obtain an arithmetic expression which can
be simplified in order to determine a final answer.
a+5b= 2 + 5 * 3
Substitution

5. Substitution Examples
If a= -2 and b= 6, simplify the following expressions:
2a + b
Step 1: Substitute a with -2 and b with 6
2 (-2) + 6
Step 2: Use your knowledge of arithmetic operations with negative and positive numbers
to simplify the expression
2 x -2= -4
-4 + 6 = 2
Therefore our ans.= 2
Remember: When
multiplying negative and
positive numbers our answer
will be negative.
When adding a negative and
positive numbers, subtract
and keep the sign of the
larger number!

6. Substitution Examples

7. Substitution Examples

8. Recap

9. Learning Resources
■ https://youtu.be/8OPEnpwIKcY
■ https://www.youtube.com/watch?v=1Zlz91YMYYg&list=PLBcP4ez7xdols
VdHOxDUIrekBc8YpZKUx
■ https://www.youtube.com/watch?v=7Qxyf-VvnPs
9

10. 10
Now that you have gained knowledge of how we substitute numbers for letters in algebraic expressions,
let’s put our knowledge to work by trying out this exercise!