When it comes to writing numbers in French, there are a good number (bon nombre) of rules to remember. Luckily, Sophie and Patrice have broken down most of them in their latest video series. They pay particular attention to the rules concerning the numeral one (un), the eighties (quatre-vingts), and the hundreds (cents).
In French, there’s only one numeral that changes according to the gender of the noun it modifies: the numeral one!
Je n’ai acheté qu’une chemise et un pantalon.
I only bought one [feminine] shirt and one [masculine] pair of pants.
This rule applies to any number ending in “one,” such as vingt-et-un (“twenty-one,” masculine) or vingt-et-une (“twenty-one,” feminine):
J’ai acheté trop de vêtements: vingt-et-une chemises et vingt-et-un pantalons.
I bought too many clothes: twenty-one shirts and twenty-one pairs of pants.
However, there’s an exception to this: the numeral un never changes when it comes after a noun indicating a number. For example:
Tournez à la page un [not: une].
Turn to page one.
Pourriez-vous me passer la revue numéro vingt-et-un [not: vingt-et-une]?
Could you pass me the magazine issue number twenty-one?
Most other numbers—from deux (two) to quarante (forty) to deux mille quarante (two thousand forty)—never change in any situation. For those that do (besides those ending in un), it’s generally a question of knowing when to add an -s at the end. Take the number quatre-vingts (eighty) for example. Quatre-vingts literally means “four twenties” (4 x 20 = 80) and always takes an -s, except—once again—after a noun indicating a number. So we would write: la page quatre-vingt (page eighty) and les années quatre-vingt (the nineteen eighties), but quatre-vingts pages (eighty pages) and quatre-vingts années (eighty years).
The -s is also dropped whenever quatre-vingts is followed by a number—as in quatre-vingt-un (eighty-one) or quatre-vingt-cinq (eighty-five):
Quatre-vingt-cinq personnes sont attendues ce soir.
Eighty-five people are expected tonight.
Did you notice we wrote quatre-vingt-un (eighty-one), but vingt-et-un (twenty-one, or “twenty and one”) above? That’s another rule of eighties and ones: you say vingt-et-un (twenty-one), trente-et-un (thirty-one), quarante-et-un (forty-one), cinquante-et-un (fifty-one), soixante-et-un (sixty-one), and soixante-et-onze (seventy-one, or “sixty and eleven”), but quatre-vingt-un (eighty-one) and quatre-vingt-onze (ninety-one, or “four-twenty-eleven” [4 x 20 + 11 = 91]).
The rules for the hundreds (cents) are the same as those for the eighties:
À chaque fois qu'il y a un nombre qui suit le cent, même s'il y a un nombre qui précède le cent, on ne met pas de S.
Each time there's a number that follows the cent, even if there's a number that precedes the cent, we don't add an S.
Cap. 43-45, Sophie et Patrice - Chiffres et nombres - Part 2
So we would write: trois cents (three hundred), la page trois cent (page three hundred), trois cent un (three hundred one; not trois cent et un!). For more on cent, and numbers like mille (thousand) and million (million), see our lesson on big numbers in French.
If your head is spinning from all these number rules, don’t fret! It’s easier to just memorize numbers like soixante-quinze and quatre-vingt-onze rather than having to calculate 60 + 15 and 4 x 20 + 11 each time you want to say "seventy-five" and "ninety-one."