Learn Turkish: Otobüste kaç yolcu var? - How many passengers are on the bus?

In Turkish, any noun that comes after a number or a quantity question word like kaç (how many) must stay in its singular form. You never add the plural endings -lar or -ler after kaç.

Why is the ending on otobüs spelled -te instead of -de?

This is because of consonant harmony. The word otobüs ends with a hard consonant (s). When the "in/on/at" suffix -de attaches to a hard consonant, its starting letter hardens to match, changing the d to a t.

How does var work in this question?

Var means "there is" or "there are". Turkish doesn't use a verb like "are" for this kind of sentence. Literally, kaç yolcu var? translates to "how many passenger(s) exist?".

Why is otobüste at the beginning of the sentence?

In Turkish, words showing where or when something happens usually go at the start of the sentence. The question word (kaç) and the noun it describes (yolcu) prefer to stay right next to each other, close to the verb (var) at the end.