This is the 2717th most frequent Portuguese word.
quantos
"Quantos" means "how many" in English.
Here, 'quantos' is used as an interrogative pronoun to enquire about the quantity of books.
Quantos livros você tem na sua coleção?
How many books do you have in your collection?
In this context, 'quantos' is used within a subordinate clause to refer to an unknown quantity of students.
Eu não sei quantos alunos virão na aula hoje.
I don't know how many students will come to class today.
In this case, 'quantos' is part of a common expression to inquire about someone's age, referencing the quantity of years.