Questions & Answers about У книзі сто сторінок.
Both у and в can mean in. Ukrainian often switches between them for ease of pronunciation and flow.
Here, у книзі sounds natural, but в книзі is also correct. This is a very common alternation in Ukrainian:
- у місті
- в автобусі
- у школі
- в Україні
So the choice is often about sound, not meaning.
Because after у / в when you mean location, Ukrainian usually uses the locative case.
So:
- dictionary form: книга = book
- locative singular: у книзі = in the book
This is why the ending changes from -а to -і.