In this video, we will be learning how to use the order of operations (PEMDAS) in word problems involving substitution. In this video we will be learning how to declare variables in word problems. After you finish this lesson, view all of our Algebra 1 lessons and practice problems.

## Example of Order of Operations with Substitution

$3x + 4y^2 - 8z$

Let $x = 5, y = -2, z=3$

Substitute first into parenthesis:   $3(5) + 4(-2)^2 - 8(3)$

Evaluate the exponent:                   $3(5) + 4(4) - 8(3)$

Multiply:                                             $15 + 16 - 24$

Addition/Subtraction:                      $31 - 24$

Simplify:                                              $7$

## Examples of Order Of Operations With Substitution

### Example 1

$2x^2 - 6y^2 + 8z$

Let $x = 4$, $y = 3$, $z=-3$

Substitute first into parenthesis:

$2(4)^2 - 6(3)^2 + 8(-3)$

Evaluate the exponent:

$2(16) - 6(9) + 8(-3)$

Multiply:

$32-54-24$

$-22-24$

Simplify:

$-46$

### Example 1

$8a+5b^2-9c^2$

Let $a=5$, $b=3$, $c=2$

Substitute first into parenthesis:

$8(5)+5(3)^2-9(2)^2$

Evaluate the exponent:

$8(5)+5(9)-9(4)$

Multiply:

$40+45-36$

$85-36$

Simplify:

$49$

## Video-Lesson Transcript

Let’s go over the order of operations with substitution.

We all know that it is PEMDAS.

Parenthesis
Exponent
Multiplication
Division
Subtraction

For example:

$3x + 4y^2 - 8z$
Let $x = 5$, $y = {-2}$, and $z = 3$

In order to evaluate this, we have to substitute these values using parenthesis.

$3(5) + 4{(-2)^2} - 8(3)$

Let’s solve the exponent part first.

$3(5) + 4(4) - 8(3)$

Then, let’s multiply.

$15 + 16 - 24$

Now, our answer is $7$.

So the key is to substitute using parenthesis. Then follow the rules in PEMDAS.