Substitution Property of Equality: Definition & Examples

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: Translational Symmetry: Definition & Examples

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
Your next lesson will play in 10 seconds
  • 0:00 Substitution Property…
  • 0:31 Why Is It Important?
  • 1:10 Examples
  • 2:32 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Speed Speed

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Karin Gonzalez

Karin has taught middle and high school Health and has a master's degree in social work.

In this lesson, you will learn the definition of the substitution property of equality and why this property is so important in mathematics. You will be given examples to illustrate.

Substitution Property of Equality

The substitution property of equality, one of the eight properties of equality, states that if x = y, then x can be substituted in for y in any equation, and y can be substituted for x in any equation.

Let's look at a quick and simple example. If we know that x = y and we have the equation x + 5 = 7, then we can substitute y for x and write the equation as y + 5 = 7.

Why is It Important?

In short, the substitution property of equality makes algebra possible. If we did not use this property in algebra, we would not be able to plug in known values for variables into mathematical expressions and equations. Even though the property is pretty easy to comprehend, it is a big deal when it comes to mathematics, especially algebra!

And why is algebra important, you may ask? Algebra is the branch of mathematics that helps us find the unknown in a mathematical expression. Usually that 'unknown' number will be represented by a letter, like x or y. Algebra is so important because it allows us to take real life word problems and write them as mathematical expressions so that we can solve them.


Example 1:

Let's take a look at a very simple example to start. Let's say that we have 5x and we know that x = 5. We can use the substitution property of equality to plug in the value of x into 5x:

So we would get 5 x 5, which is 25!

Example 2:

Let's look at the expression:

4x + 5y + 2p

We know that:

x = 2

y = 1

p = 3

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account