Positive & Negative Positive & Negative Numbers.Numbers.

Adding and Subtracting.Adding and Subtracting.

What’s The Missing Number ?

(1) – 6 + = 12

(2) + 10 = – 3

(3) 12 – = – 22

(4) – 14 = – 25

(5) 22 – = – 17

18

-13

34

-11

39

This is a revision of number facts you already know.

Complete

Some New Rules.Some New Rules.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 = Is the same sum2

The same rule applies for taking away a positive.5 – + 8 = Is the same as 5 – 8 = –3

Subtracting A Negative Subtracting A Negative Number.Number.Five judges have to give a score of between –10 and 10 in a

ball throwing competition.

Here are the judges scores.

– 4 6

– 7 3 – 2

Add up the total score : – 4

The rules say that the lowest score is always removed.

What score is this ? – 7

– 4 6 3 – 2

Now add up the new total:

3

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 :

– 4 + 7 = 3

Rule 2 : Subtracting a negative is the same as adding the number on.

What a dastardly good rule !!

Some Worked Examples.Some Worked Examples.

Calculate :

( 1) 6 + - 7 = 6 – 7 = -1

( 2) 4 - - 9 = 4 + 9 = 13

( 3) -3 + - 7 = -3 – 7 = -10

( 4) 2 - + 5 = 2 – 5 = -3

( 5) -7 - - 7 = -7 + 7 = 0

What Goes In The Box ?What Goes In The Box ?

( 1) – 5 + – 6 =

(2) 6 + – 4 =

(3) 8 – – 7 =

(4) – 3 – + 8 =

(5) 12 – (– 6 ) =

Is the same as :

– 5 – 6 =

6 – 4 =

8 + 7 =

– 3 – 8 =

12 + 6 =

-11

2

15

-11

18