Addition and subtraction of negative numbers Dont panic

Addition and subtraction… …of negative numbers

Don’t panic! I’ll lead you through it

We are all familiar with addition and subtraction of positive numbers as we have been performing calculations like that since Primary school

And even 7 – 4 =…. . 3

Most of us will accept that -5 + -2 = -7

No problem Feel free to ask questions if you don’t understand something

- 5 + -2 = -7 • I will show -5 as five tiles, each with a value of -1 -1 -1 • I will now add another -2 (two tiles) as the question demands -1 -1 -1 • We now have a total of -7 -1 -1

Are you all happy that this is the same as -5 -2 = -7 ?

I am going to assume that we are all happy that -1 and +1 together have a value of zero The total of value of these numbers is zero -1 +1 -1 -1 +1 +1

-5 - 2 = -7 • Start with tiles with a total value of -5 -1 -1 -1 +1 +1 +1 -1 -1 -1 • Now ‘subtract 2’ (two blue tiles) -1 • +1 -1 -1 You are left with a total of -7

But what about those ‘double negatives’ such as …. ? -3 - - 1

-3 - -1 I will set out some tiles with a total value of -3 -1 -1 +1 +1 -1 -1 -1

-3 - -1 Now I will subtract a ‘-1’ tile as the problem demands

-3 - -1 -1 +1 We are left with tiles with a value of -2

So -3 - -1 = -2

Now some for you to try….