Questions & Answers about I biglietti e i documenti sono qui.
Why do biglietti and documenti both end in -i?
Why is the word i used before these nouns instead of il?
i is the plural form of the word "the" for masculine nouns that start with most consonants. Since the singular forms use il (il biglietto and il documento), their plural forms use i (i biglietti and i documenti).
Why do we repeat the word i? Could I just say "i biglietti e documenti"?
You really need to repeat it! In English, we often say "the tickets and documents" and drop the second "the". In Italian, you almost always have to repeat the definite article before every single noun in a list.