Skoool Kerala

Positive and Negative Numbers

Number Line: -10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0 1 2 3 4 5 6 7 8 9 10

This is a section of the number line from –10 to + 10.

Note, we can write positive numbers without the + sign.

With these numbers we will have double signs: + –, + +, –  – and – +

It is easier to replace these with single signs: + or –

– + can be replaced with –

+ + or –  – can be replaced with +

Example 1:

6+ – 4 = 6 – 4 = 2 

6 – + 4 = 6 – 4 = 2 

6 + + 4 = 6 + 4 = 10

6 –  – 4 = 6 + 4 = 10

Rule: If the double signs are different, they are –

If they are the same, they are +

We can now add and subtract on the number line.

Example 2:

4 – 7 = –3

We start at 4 on the number line and move 7 places to the left, as illustrated below.

–3 + 7 = 4

We start at –3 and move 7 places to the right, as shown below.

–1 – 5 = –6

We start at –1 and move 5 to the left.

Rule: Start with the first number and move right for + and left for – 

Multiplying and Dividing

We need to learn two new rules.

Rule 1: When multiplying or dividing two numbers with the same signs we get a positive number.

For example, +3 x +5 = +15; –3 x –5 = +15; +6 ÷ +3 = +2;

-6 ÷ –3 = +2

Rule 2: When multiplying or dividing two numbers with different signs we get a negative number.

For example, +3 x –5 = –15; –3 x +5 = –15; 6 ÷ –2 = -3; –6 ÷ 2 = –3