Not "4×20", but "4 20", and in a single word that means "80" without thinking about 4 and 20.
When you say eighteen, you think just "18" and not "8 teens". (Similarly, when you say "backwards" you think of the direction, not of "back wards")
When you say eighteen, you think just "18" and not "8 teens". (Similarly, when you say "backwards" you think of the direction, not of "back wards")
https://en.wiktionary.org/wiki/quatre-vingts#French