The numbers 70-99 follow a pattern that, in a very general sense, requires mastery of the numbers 1-20. All of the parts used in these numbers are also individual numbers themselves. As such, they follow the same pronunciation rules as seen before.

Note that the number 80 has a final ‘s’. For numbers ending with ‘-un’, the grammatical gender of any associated noun needs to be considered. If that noun is grammatically feminine, then ‘-une’ is required. This is similar to the usage of indefinite singular articles. The number 81 does not use ‘et’ in its construction, unlike other numbers ending with ‘-un’.

e.g.

In some parts of the French-speaking world, particularly in Acadia, Belgium and Switzerland, the numbers 70, 80 and 90 each have a different unique form, which is then just combined with the numbers 1-9. These forms, however, are generally considered incorrect by speakers from outside these areas.