Choose the Best Method to Add Numbers Mentally

We are going to look at solving addition questions mentally.

This means that we need to find the answers using just our brains!

Luckily, there are lots of different strategies we can use to help us.

 

In this activity, we are going to look at adding to the next ten before adding the remainder of the number. 

We will also look at how we can use bonds to ten.

 

Adding to the next ten, then adding the remainder

We can use this method for addition questions such as 16 + 7

We know that we can partition 7 like this: 4 + 3  = 7

So, we can make the next multiple of ten by adding  4 to 16  ( 16 + 4 = 20 )

Then we need to add the remaining 3 to 20  ( 20 + 3 = 23 )

16 + 7 = 23

 

Let's have a look at another example.

 

47 + 8 

We know that we can partition 8 like this  3 + 5 = 8

So, we can make the next multiple of ten by adding  3 to 47  ( 47 + 3 = 50 )

Then, we need to add the remaining 5 to 50  ( 50 + 5 = 55 )

47 + 8 = 55

 

 

Pairs to ten

Where digits add up to 10 we can use this to help.

34 + 46 =

30 + 40 = 70

4 + 6 = 10

70 + 10 = 80

 

Let's have a look at another example.

 

245 + 135 =

240 + 130 = 370

5 + 5 = 10

370 + 10 = 380

 

Now, why don't you have a go at answering some mental addition questions using these strategies?

You might already know some other strategies that work well for you too!