Today I've heard a talk about division rules. The lecturer stated that base 12 has a lot of division rules and was therefore commonly used in trade.
English and German name their numbers like they count (with 11 and 12 as exception), but not French:
# | English | German | French
-----------------------------------------------
0 | zero | null | zero
1 | one | eins | un
2 | two | zwei | deux
3 | three | drei | trois
4 | four | vier | quatre
5 | five | fünf | cinq
6 | six | sechs | six
7 | seven | sieben | sept
8 | eight | acht | huit
9 | nine | neun | neuf
10 | ten | zehn | dix
11 | eleven | elf | onze
12 | twelve | zwölf | douze
13 | thir|teen | drei|zehn | treize
14 | four|teen | vier|zehn | quatorze
15 | fif|teen | fünf|zehn | quinze
16 | six|teen | sech|zehn | seize
17 |seven|teen | sieb|zehn | dix-sept
18 and 19 are "regular"
20 | twenty | zwanzig | vingt
21 |twenty-one | ein|und|zwanzig | vingt et un
22 |twenty-two | zwei|und|zwanzig | vingt-deux
23 - 69 are "regular"
70 | seven|ty | sieb|zig | soixante-dix = 60 + 10
....
80 | eigh|ty | acht|zig | quatre-vingts = 4*20 ?!?!
81 |eighty-one | ein|und|achtzig | quatre-vingt-un = 4*20 + 1
...
So my question is:
Why do French count so strangely after 79?
(Are there other languages that count similar? What's the historic / mathematical reason for this system?)
one, two, ..., nine, ten, ten one, ten two, ..., ten nine, two ten, two ten one, two ten two, ..., ..., nine ten nine, hundred, hundred one
. It makes learning to count in japanese, as simple as learning0-10
,100
,1,000
, and10,000
. $\endgroup$