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Number Systems
Numbers can be classified into various groups or sets:

The positive numbers are those greater than zero.They can be written with a ‘+’ in front such as +6, +2.4, +2/5, or they can be written without a sign, for example, 5, 7.3, 8/9

The negative numbers are those less than zero.Negative numbers are always written with a minus sign, ‘‘ , in the front of it, for instance, 4, 0.65, 3/5.

The natural numbers, or counting numbers, are: 1, 2, 3, 4, 5.....

The whole numbers are the natural numbers, together with zero: 0, 1, 2, 3, 4, 5.....

If we consider the negative as well as positive whole numbers, these are known as the integers: 3, 2, 1, 0, 1, 2, 3.....

Through the introduction of fractions, the number system can be extended and all numbers that can be expressed in the form a/b, where ‘a’ and ‘b’ are integers and ‘b’ does not equal zero, are called rational numbers.This group will include the integers themselves since, for instance, 5 = 5/1 and 7 = 7/1 and so the integers can be expressed in the form a/b.
Exercise:
Work through the exercise below.
Use these numbers to answer the questions:
3, 7, ¾, +4, 723, ½, 1.75, 500, +18, 0,
List:

All the positive numbers

All the natural numbers

All the whole numbers

All the negative numbers

All the integers

All the fractions
Answers below:
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7,+4, 723, 500, +18

7,+4, 723,500, +18

0,7, +4, 723,500, +18

3,½, 1.75,

0, 3, 7, +4, 723, 500, +18

3, 7, +4, 723, ½, 1.75, 500, +18 (includes integers except 0 since they too can be expressed in the form a/b)