"Wanasoma kitabu changu."

Translation: They read my book.

[TrackAttack2]

Why is it changu instead of yangu? They both seem to mean my/mine, right?

[ElMeuNom]

Noun class. Ki/Vi nouns take changu in the singular (chake, chako, etc.) and vyangu in plural (vyake, vyako, etc.) Yangu (yake, yako, etc.) is used for M/Mi and Ji/Ma in the plural and N/N in the singular.