Questions & Answers about Das Buch hat dreißig Seiten.
Why is 30 spelled with an ß (dreißig) instead of a z like the other tens?
It is a special exception! While 20 (zwanzig), 40 (vierzig), and 50 (fünfzig) all end in -zig, 30 is the only ten that ends in -ßig. You just have to memorize this spelling quirk.
What is the singular form of Seiten (pages)?
Why do we use hat here instead of haben?
Das Buch (the book) is the subject of the sentence, acting as a singular it (es). The verb haben (to have) is irregular, and its he/she/it form is hat.
Why is it das Buch and not der Buch or die Buch?
In German, every noun has a grammatical gender. Buch is a neuter noun, so it takes the neuter word for the, which is das.