"Why are you so tired?"
Translation:Czemu jesteście takie zmęczone?
Czemu nie dlaczego zamiast czemu?
Both are accepted, "czemu" was just the choice of whoever created the sentence :)
Is there a situation where one would use czemu instead of dlaczego or are they interchangeable? For example, in formal conversation or something like that?
They are interchangeable, but some people may find 'czemu' a bit colloquial.
What's the difference in this context for "takie zmęczone" and "tacy zmęczeni"?
in all contexts:
takie zmączone is about a group you would refer to as one = not masculine personal
tacy zmączeni- is about a group you would refer to as oni= masculine personal
oni są tacy zmęczeni
one są takie zmączone
if you need a remind:
oni= masculine personal- group of people that include at least one male person, unspecifiedgroup of people referred to using masculine noun, group that include at least one person and at least one male animal.
one= not masculine personal - feminine and neuter nouns, masculine nouns that do not describe people, groups of only female people.