"You heat the butter, I cool the cheese."
Translation:Tu încălzești untul, eu răcesc brânza.
There is no mistake. It is correct with ”tu”. Without ”tu” would sound ok as well but then the ”eu” has to stay in. As we do not know the context, I guess both ”tu” and ”eu” have to be present in this sentence. Though, I cannot explain why.
If you could leave the 'tu' away, then 'încălziți' shold also be a correct answer. In that case you just leave away a 'voi', which is not even among the words they propose. But still the you in english doesn't define, if it's a plural or a singular. So 'încălzești' and 'încălziți' should be correct. There are a lot of other examples here, where the correct answer proposed by duolingo leaves away the 'tu' or 'voi'. So why not here? And why is 'încălziți' is regarded as wrong here?
I agree that for English "you", both forms (singular and plural) should be accepted as correct translations. Of course, when the context does not specify it. In Romanian, some sentences sound weird without the pronoun. This is one of the examples.