Lesson 7 — Activity 2: Simple Substitution



Getting Ready


In algebra, when you "substitute", this simply means that you are putting numbers in place of the variable (the letters). In this lesson, you will learn about simple substitution in algebraic equations.


Courtesy of ADLC

One of the basic steps in algebra is simple substitution. Simple substitution means that you have an equation with a variable and you are given a value (number) for that variable.

Here is an example of simple substitution:

If x = 2, what is 100 + x?

To solve this, you simply substitute in the value (2) for the variable (x) so that the question now reads:

What is 100 + 2?

Of course, the answer is 102!
Sometimes in algebra, when you multiply, the constant and variable don't have a sign between them. In the example below, it is understood that you need to multiply 10 and the value for w.

If w = 5, what is 10w?

You do the same thing as you did when you were adding. Substitute the 5 for the w. The question now reads:

What is 10 x 5?

Of course, the answer is 50!

Can you see that there could be confusion between the x for multiplication and an x as a variable?

There are two ways to avoid this.

1. Put the 5 in brackets like this, 10(5) = 50.

OR

2. Put a multiplication sign in front of the 5 like this, 10 x 5 = 50.

Both are correct. It is up to you to decide which works best for you.

Here is an example of multiplying using simple substitution:

If g = 100, what is 4g?

4(100) = 400
OR
4 x 100 = 400


Now let's take a look at an example of simple substitution with division.

If x = 4, what is 100 ÷ x?


    100   
4

OR

100 ÷ 4 = 25


  Self-check!

Try this!

Solve the following equations using simple substitution.

1. If p = 50, what is p + 50?
2. If y = 30, what is 40 – y?
3. If h = 3, what is 7h?
4. If a = 64, what is a ÷ 8?


1. 50 + 50 = 100
2. 40 – 30 = 10
3. 7(3) OR 7 x 3 = 21
4. 64 ÷ 8 = 8


Digging Deeper


Click on the Play button below to watch a short video on simple substitution in algebra.