"That hat is bigger."
Translation:Acea pălărie e mai mare.
I'm learning here on Duolingo and I have no experience in Romanian, but I googled a bit on the subject and from what I understand the informal forms of that/those which are:
ăla - singular, masculine (that)
aia - singular, feminine (that)
ăia - plural, masculine (those)
alea - plural, feminine (those)
can only be used in post-position, meaning they can only go after the noun. With the regular ones (acela, aceea, aceia and acelea) you just remove the final -a whenever you want to use them before the noun (acel, acea, acei and acele), but with those informal ones you can't do that, so they always go after the noun.
So I believe the correct way to use "aia" in this sentence would be:
"Pălăria aia este mai mare."
I do not know if that is a valid answer according to Duolingo, but it should be.
However, it seems like the informal forms of this/these do have a pre-position (formed once again by the removal of an -a), however according to Wikipedia the pre-position versions are used very rarely:
ăst (pre-position) - ăsta/ista (post-position) - singular, masculine (this)
astă (pre-position) - asta (post-position) - singular, feminine (this)
ăști (pre-position) - ăștia (post-position) - plural, masculine (these)
aste (pre-position) - astea (post-position) - plural, feminine(these)
Duolingo does a great job of teaching us a lot of words and constructions, but there are a lot of details that are not explained well enough. But maybe that's because Romanian is still in beta.
If someone who's a native or has more experience feels like what I said is incorrect, please correct me as I am also trying to understand this quite difficult lesson.