Learn Croatian: Imam pet sestara. - I have five sisters.

In Croatian, numbers from five onwards (5, 6, 7, 10, 100, etc.) require the noun following them to be in the genitive plural case. Since we have pet (five), we use the genitive plural form sestara instead of the regular plural sestre (which is only used for numbers 2, 3, and 4).

Where does the extra 'a' in the middle of sestara come from?

This is a special pronunciation rule for the genitive plural case. When a noun's base ends in two consonants (like the 't' and 'r' in sestra), Croatian often inserts a 'fill vowel' (an extra 'a') between them in the genitive plural to make the word easier to pronounce. So sestra becomes sestara, just like djevojka (girl) becomes djevojaka.

Does the number pet change its ending depending on the sentence?

No, it does not. In Croatian, numbers from five onwards do not decline (they do not change their endings). The word pet stays exactly the same regardless of its grammatical role in the sentence. Only numbers one through four change their forms.

Why is there no word for 'I' (ja) before imam?

The verb form imam already contains the meaning 'I have'. In Croatian, it is completely standard to drop subject pronouns like ja (I) or ti (you) unless you want to emphasize who is doing the action, for example: 'I have five sisters, but he only has one'.