Questions & Answers about Marias mobil är ny, men de gamla mobilerna är mina.
Why do we use both de and -erna in de gamla mobilerna?
This is the double definiteness rule for plurals! When you have a definite noun described by an adjective, you need a free article (de for plurals) before the adjective, AND the definite suffix on the noun itself (-erna). It is like saying 'the old the cell phones'.
Why is the first adjective ny but the second adjective is gamla?
Adjectives must match their noun. Because mobil is singular and an en-word, we use the basic form ny. However, mobilerna is plural and definite, so the adjective must take the -a ending. The word gammal (old) is slightly irregular and drops some letters to become gamla.
Since we are talking about Maria's specific phone, why isn't it Marias mobilen?
In Swedish, whenever you use a possessive word or a name ending in an ownership -s (like Marias), the noun that follows must stay in its indefinite form (mobil). The ownership word already makes it definite enough!
Why do we use mina instead of min at the end of the sentence?