Definition and calculation methodThe numbers which are on the left of the number 0 are called negative numbers.
The numbers which are on the right of the number 0 are called positive numbers.
Integers are every positive and negative numbers.
To add or subtract two positive or negative numbers :
1. You place the first number on the line above.
2. Then if there is a + sign you move towards the right, if there is a - sign you move towards the left.
3. You move towards the right or towards the left of the second number.
To calculate 1 + 3, you first place the number 1 on the drawing (in green on the picture), then as there is the sign + you move towards the right and then as there is the number 3 you move 3 steps forward. You land on the number 4. Therefore 3 + 1 = 4. This method also works for more complicated calculations.
To calculate - 3 - 2 , you first place the number - 3 then as there is the sign - you move towards the left and then as there is the number 2 you move 2 steps on the left. You land on the number - 5 therefore - 3 - 2 = - 5.
To calculate 4 - 5 the result is not 1 because if you have a 4 dollars and you spend 5 dollars you cannot have 1 dollar left. You place yourself on 4 and you move 5 steps on the left because it is a negative sign -. We land on -1 therefore 4 - 5 = -1.
Final example : to calculate - 5 + 3, you place yourself on - 5 and you move forward 3 steps on the right (sign +), you land on the number -2, so - 5 + 3 = -2.
When the signs follow each other :
When two + signs follow each other, it is as if there were only one + sign +
If a - sign and a + sign follow each other or vice versa, it is as if there were a - sign
If two - signs follow each other, it is as if there were a + sign.
You must always put brackets between two signs which follow each other.
3 + (+3) = 3 + 3
4 - (+7) = 4 - 7
-2 + (-1) = - 2 - 1
- 5 - (-8) = - 5 + 8
5 - (+6) = 5 - 6
You can complete the last stage of the calculations by drawing the grduated line and following the above method. We respectively get the following results: 6, - 3, - 3, 3, and -1.
See also : integers on fmaths.com