Questions & Answers about Odkurzajmy nasz stary garaż raz w miesiącu!
Why do we say w miesiącu for 'a month' here?
To express frequency like 'once a month', Polish uses raz (once) + w (in/per) + a time period. The word miesiąc (month) takes the Locative case here, becoming miesiącu. Other time units like rok (year) or tydzień (week) also use the Locative in these phrases (w roku, w tygodniu).
How does the word odkurzajmy mean 'let's vacuum'?
This is the imperative (command) form for 'we'. You form it by taking the informal 'you' command form, which is odkurzaj (vacuum!), and adding the 'we' ending -my. This turns a direct command into a suggestion for the group.
Could we use a perfective verb for 'let's vacuum' in this sentence?
No, we must use the imperfective verb odkurzać (here as odkurzajmy) because we are talking about a repeated, regular habit. The phrase raz w miesiącu (once a month) requires an imperfective verb, whereas perfective verbs are for single, completed actions.
Isn't nasz stary garaż the direct object? Why doesn't it have an Accusative case ending?
It actually is in the Accusative case, but it looks exactly like the basic Nominative dictionary form! That is because garaż is a masculine inanimate noun (a masculine 'thing'). For masculine inanimate nouns, the Accusative case is identical to the Nominative case, so both the noun and its adjectives (nasz stary) do not change their spelling here.