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### 10 (ten)

The **number 10** plays a central role in all cultures, because we have ten fingers.

##### Numeral system

We work with the decimal system, and use the Arabic numerals

0, 1, 2, 3, 4, 5, 6, 7, 8, 9

##### Numbers

Behind each digit in a decimal number is a power of 10 that depends on the position. You must write a 0 if a place has no value. We count 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, ... and so on.

##### Common logaritms

Base-10 logarithms were widely used before calculators were available. There were so called logarithm tables in which you could look up the result. These logarithms are called common logarithms, and can be written as

log (

x) or log_{10}(x) or^{10}log (x) and sometimes also as lg (x)

##### Tetractys

The number 10 was the symbol of the completion for the ancient Greeks. With dots you can draw this number as a triangle.

••••••••••

They called it the tetractys, and you can calculate it as 1 + 2 + 3 + 4 = 10.