Find the Unknown Number in an Equation

In this activity, we will be finding unknown numbers in equations. 

 

You probably remember doing these when you were very little!

 

 

You had to write down the missing number in the box!

To work out this simple problem you would do 6 - 4 = 2 in your head in seconds.

 

Algebra is exactly the same and is that simple.

We just replace the box with a letter, like this:

 

 

We solve this in exactly the same way:

a = 6 - 4

a = 2

 

Easy, right?

 

 

It works for this too!

 

 

4 x something = 12

We would do this by dividing 12 by 4 = 3

Let's write it with a letter instead of a box again!

 

 

Same way again:

y = 12 ÷ 4

y = 3

 

Easy!

 

As mathematicians, we like to simplify things and make life easier for ourselves so we shorten:

 

4 x y to 4y

 

In other words, we do not write the multiplication sign!

So, 2 x c = 2c

7 x u = 7u
 

Let's have a go at finding some of these unknown letters then!

Remember, we use the inverse to solve these.