Look at these sentences using approximate numbers:
In French, to express an approximative number (ten or so, about fifteen...), you can add une/deux/trois ... in front of the number and the suffix -aine at the end of it, as follows:
|10 / dix||une dizaine|
|12 / douze||une douzaine|
|15 / quinze||une quinzaine|
|20 / vingt||une vingtaine|
|30 / trente||une trentaine|
|40 / quarante||une quarantaine|
|50 / cinquante||une cinquantaine|
|60 / soixante||une soixantaine|
|100 / cent||une centaine|
This is the equivalent in English of saying ten or so, around twenty, or fifteen odd. As in English, douzaine (dozen) means 12 rather than being an approximate number, but the construction is the same as for approximate numbers.
Note: These approximate numbers are feminine, and followed by de.
ATTENTION: Whereas you'd tend to say in English dozens and dozens, in French the use of dizaine (ten or so) will be more colloquial: des dizaines et des dizaines.