"The tall girls are the new musicians."

Translation: A magas lányok az új zenészek.

[btiirwin]

Is it really wrong to add a 'vannak' at the end of this sentence?

[vvsey]

Yes, it is absolutely wrong. It is not optional, it is wrong in this case.

Mi zenészek vagyunk.
Ti zenészek vagytok.
Ők zenészek.

[btiirwin]

In some places it seems ok to use van/vannak, but in other places it is wrong. How do you distinguish between them?

[mizinamo]

Use van/vannak when describing where something is or when using an adverb (e.g. "She is fine" - Jól van).

Do not use van/vannak when describing what something is (Az egy könyv "that is a book") or what its attributes are (A könyv piros "the book is red").

[btiirwin]

Very helpful, thank you!

[JeanMencze]

OK - now I understand it too!

[Andrew359786]

If they are lányok, shouldn't they be zenésznők?

[vvsey]

There is no such word in Hungarian. Only a few professions/occupations make that distinction. It is basically irrelevant in this case, so there is no separate word.

[Charmian280720]

Mizinamo, thank you. That explanation is clear and so helpful. Köszönöm szépen