Learn Italian: Il mio gruppo ha tredici persone.

In Italian, you almost always need to use a definite article (like il or la) before a possessive word (like mio). You literally say "the my group." The main exception is when talking about singular family members, like mio padre (my father).

Does tredici change its ending depending on what we are counting?

No, numbers from two upwards never change their endings to match the gender or number of the noun. Whether you are counting masculine objects or feminine nouns like persone, it is always tredici.

How is the word tredici formed?

For the numbers 11 through 16, Italian puts the single digit first, followed by -dici (meaning ten). So three (tre) plus ten (dici) becomes tredici. Be careful: this pattern flips starting at 17 (diciassette), where the "ten" part comes first!

The word persone is feminine plural. What if the group consists of men?

The word persona (person) is always grammatically feminine in Italian, regardless of the person's actual gender. Therefore, its plural form persone is always used, even if the group is entirely made up of men.

Is the "h" in ha pronounced?