Questions & Answers about Mä tiiän, et toi kammio ois koristeltu heti.
The lesson is about the conditional perfect passive. How is it formed in this sentence?
The conditional perfect passive is formed using the conditional form of the auxiliary verb olla (here, the spoken form ois instead of olisi) plus the passive past participle of the main verb (koristeltu). Together, ois koristeltu means "would have been decorated".
How do we form the passive past participle koristeltu from the dictionary verb koristella (to decorate)?
Koristella is a Type 3 verb (verbs ending in -lla or -llä). For these verbs, forming the passive past participle is very straightforward: you simply drop the final -a or -ä and replace it with -tu or -ty. Therefore, koristella becomes koristeltu.
This sentence looks very different from standard written Finnish. What are the standard forms?
Almost every word here is typical spoken Finnish! The standard written version would be: Minä tiedän, että tuo kammio olisi koristeltu heti. Notice how mä (minä), tiiän (tiedän), et (että), toi (tuo), and ois (olisi) have all been shortened.