"The cows are big and fat."
Translation:Vacile sunt mari și grase.
I think it is 'mari' with an 'i' because it is one of the few cases in Romanian in which an adjective only has two forms (sing: mare, pl: mari), regardless of gender; so in this case, despite 'vacile' being fem pl, the right form is 'mari'. On the other hand 'grase' is the form for fem and neuter pl so that is the form which one has to use for this sentence. So that is why one of them ends 'i' and the other one 'e'.