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### Number

Numbers are not apparent in nature as physical entities.

##### Explanation

A number can contain digits, letters and symbols. They are often used to indicate a position within a hierarchy, as for house numbering. But sometimes there is not even an hierarchy as with telephone numbers.

##### Representations

Sometimes, numbers are represented as beads on a string. Each bead has a number, and so you get a kind of number line. It looks like a rosary. That image can be used for simple calculations. It can also lead to confusion.

The addition 1/2 + 1/2 = 1 cannot be explained by this, allthough a child will understand it. Maybe there are large and small beads?

Use images and pictures only if they help. But always keep in mind that applies: a number is a number. That is all.

##### Example 1

Numbers are no points. You can write the number 1 as 0.999... and then you don't know if this is the same point. If you delete the point 1 will the point 0.999... then remain or does it disappear aswell?

##### Example 2

You can indicate numbers with letters. You call this the number x, a, e, i or π, etc. It often involves constants, variables, or parameters.

##### Example 3

A number can be written as

12        2,5         8 1/2        0,9999...      6a2        √2

A house number can be written as

12A

A telephone number can consist of

A flight number can be

B 3752 HL