Find the Value of an Expression by Substituting a Variable

In this activity, we are going to work out the value of an expression by using substitution.

 

From football, we know that substitution is just swapping one player for another.

We do this in maths, but we swap an unknown for a value.

 

 

For example:

If n = 6, what is the value of n - 2?

We swap the n with 6

n - 2 = 6 - 2

= 4

 

Easy right?

 

What about this one?

 

Example

If a = 5, what is the value of 3a + 4?

 

Answer

3a + 4 means 3 x a + 4

When a = 5 we can write

3 x 5 + 4 = 19

 

Let's try some!