Learn Italian: Ripassando per l'esame, abbiamo trovato un grande errore. - Reviewing for the exam, we found a big mistake.

The gerund ripassando (reviewing) acts as a clause that tells us when or how the main action happened. In Italian, you can use the present gerund like this as long as the subject doing the gerund (we) is the exact same as the subject of the main clause (abbiamo trovato). It works just like saying "while reviewing..." or "upon reviewing...".

Can ripassare mean things other than studying?

Yes! While here it means "to review" or "to revise" for an exam, its literal meaning is "to pass again" (ri- + passare). You will often hear it used in daily life to mean dropping by a place again, such as ripasso più tardi (I will come by again later).

Why is the adjective grande placed before the noun errore?

Most adjectives in Italian go after the noun, but very common ones like grande (big) and piccolo (small) often go before it. Placing grande before the noun also highlights the figurative importance of the word, meaning this is a "major" or "serious" mistake, rather than something physically large.

Why does the main clause use the passato prossimo (abbiamo trovato) rather than the imperfetto?