Linguistics
French counts 80 as 'four twenties' — a fossil of counting by scores
In French, eighty is 'quatre-vingts' (four twenties) and ninety-seven is 'quatre-vingt-dix-sept' (four-twenty-ten-seven). It's a leftover of the vigesimal, base-20 counting system used before Latin numerals took over. Belgian and Swiss French mostly dropped it for 'septante' and 'nonante', but standard French kept the base-20 fossils in its 70s, 80s and 90s.