"How many sheets of paper are in the envelope?"

[luca.anceschi]

"Quanti fogli di carta ci sono nella busta" is definetely an option.

[siebolt]

Yes and no. If you add "ci" I would expect "there" in the English sentence.

[luca.anceschi]

I got your point albeit somehow I disagree. The relation between english and italian in this case is not 100% one to one imho.

[siebolt]

I would have used "ci" without thing twice.