Questions & Answers about Wystawa jest czynna od wtorku do piątku.
Why do wtorek and piątek change to wtorku and piątku here?
The prepositions od (from) and do (to) both require the Genitive case. For the days wtorek (Tuesday) and piątek (Friday), adding the Genitive ending -u causes the "mobile e" in the final syllable to drop out, resulting in wtorku and piątku.
Why use czynna for "open" instead of otwarta?
While otwarta literally means "open" (like an open door or window), czynna means "active" or "in operation". In Polish, establishments like exhibitions, shops, or offices are usually described as czynne when they are open to the public.
Can I use z instead of od for "from" in this sentence?
No, when talking about a span of time (from [start] to [end]), you must always use the specific pair od ... do .... The preposition z (which can also mean "from") is mostly used for physical movement out of a place.
Why does czynna end in -a here?