1. Numbers Working with negative numbers

2. Numbers There are many different ways of adding and subtracting negative numbers; we all have different methods we prefer. The following slides will show some techniques you may not have seen before. Hopefully this will help in the next challenge.

3. Numbers Adding two numbers together is simple and can be done either way round: 4 + 7= 117 + 4= 11 As soon as we subtract numbers however, it DOES matter which way round they go: 4 - 7= 37 - 4= -3

4. Numbers Try working with a thermometer. - 4 - 5 0 -2 -3 -4 -5 -6 -7 -8 -9 -10 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Start on the thermometer at the first number Subtract 5 means you will drop down even further to - 9

5. Numbers Try this one - 2 + 8 = ? 0 -2 -3 -4 -5 -6 -7 -8 -9 -10 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0 Start on the thermometer at the first number Add 8 means the temperature increases to …….? + 6

6. Numbers Lets just look at the subtraction again a bit more carefully Notice that the resulting numbers are the same, it is just that when we take the larger number from the smaller number, the result is a negative number. We can use this to make life a lot easier for ourselves. 4 - 7= 37 - 4= -3

7. Numbers 5 - 12= 712 - 5= -7 Have a go at these 22 - 27= -96 - 15= -5 so 24 -137= -1336 - 49= -113

8. Numbers What about this business with loads of + and – calculations? - 7 + - 4 We can look at this thinking about temperature. -7 0 C add -4 0 C (which means adding more cold air) will bring down the temperature even lower to -11 0 C

9. Numbers There is a quick alternative – but you have to learn it and be very careful with it. - 7 + - 4 + + is the same as just + - - is the same as just + + - is the same as just – - + is the same as just –

10. Numbers Many of you will recognise this from multiplying positive and negative numbers. - 7 + - 4 Is the same a -7 - 4= -11 4 - - 8 Is the same a 4 + 8= 12

11. Numbers To get good at this you have got to be able to practise…. Regularly. No homework? Then randomly make up addition and subtraction calculations with different combinations of positive and negative numbers. Check you are getting them right with a calculator

12. SIMPLES!