Add Numbers Mentally

In this activity, we will be adding numbers mentally. 

 

Let's remind ourselves what it means to do something mentally.

It means that we work it out in our heads (but don't forget we can always use our fingers to help us!) 

 

We will be adding two-digit numbers with ones and we will be adding two-digit numbers with tens. 

Let's have a look at what all this means!

 

 

Adding two-digit numbers with ones 

A two-digit number is any number made up of two digits, so that's all the numbers between 10 and 99! 

 

Ones are all the one-digit numbers, so that's all the numbers from 0 - 9. 

 

Let's have a look at an example question and how we could answer it:

46 + 7 = 

 

Here are the steps we need to take to answer this mentally:

 

- Put the biggest number in your head, so that's 46 

- Hold up 7 fingers ready to count on 

- Now count along 7 from 46 using your fingers to help you keep track:

47, 48, 49, 50, 51, 52, 53

 

We have landed on 53, so 46 + 7 = 53 

 

Adding two-digit numbers with tens 

A two-digit number is any number made up of two digits, so that's all the numbers between 10 and 99! 

Tens are all the multiples of tens (which are the numbers in the 10 times tables)

They are 10, 20, 30, 40, 50, 60, 70, 80, 90 and 100. 

 

Let's have a look at an example question and how we could answer it:

46 + 30 = 

 

Here are the steps we need to take to answer this mentally:

 

- Put the biggest number in your head, so that's 46 

- Hold up 3 fingers ready to count on 3 tens

- Now count along 3 tens from 46 using your fingers to help you keep track:

56, 66, 76

 

We have landed on 76, so 46 + 30 = 76

 

Remember when we are adding on 10s all the 10s numbers have no ones, so the ones number will always stay the same!

 

 

Now, let's have a  go at some questions.