1. Positive & Negative Numbers.
Adding and Subtracting.

2. What’s The Missing Number ?
This is a revision of number facts you already know.
Complete
(1) – = 12 18
(2) = – 3
-13
(3) 12 – = – 22 34
(4) – = – 25
-11
(5) 22 – = – 17 39

3. Some New Rules. 6 + 6 2 What happens if you add a negative number ?
Consider the sum below : 6 +
– 4 =
Rule 1 : Adding a negative number is just the same as taking away that number. Hence: 6
– 4 = 2
Is the same sum
The same rule applies for taking away a positive.
5 – + 8 =
Is the same as
5 – 8 = –3

4. Subtracting A Negative Number.
Five judges have to give a score of between –10 and 10 in a ball throwing competition.
Here are the judges scores.
– 4
– 7 3
– 2 6
– 4
Add up the total score :
The rules say that the lowest score is always removed.
What score is this ?
– 7
Now add up the new total: 6 3
– 4 3
– 2

5. Consider the sum below :
Old score
Minus lowest score
Equals new score.
Put the numbers in place of the statements:
– 4 –
– 7 3 =
That is to say :
– 4 – ( – 7 ) = 3
Which is the same as :
– = 3

6. Rule 2 : Subtracting a negative is the same as adding the number on.
What a good rule !!

7. Some Worked Examples. -1 ( 1) 6 + - 7 = 6 – 7 = 13 ( 2) 4 - - 9 =
Calculate : -1
( 1) =
6 – 7 = 13
( 2) =
4 + 9 =
-10
( 3) =
-3 – 7 =
( 4) =
2 – 5 = -3
( 5) = =

8. What Goes In The Box ? Is the same as : – 5 – 6 = -11 ( 1) – 5 + – 6 =
( 1) – 5 + – 6 =
6 – 4 = 2
(2) 6 + – 4 =
8 + 7 = 15
(3) 8 – – 7 =
– 3 – 8 =
-11
(4) – 3 – + 8 = = 18
(5) 12 – (– 6 ) =