Question

question: algo mas grande que un elefante

answer: unas casas son mas grande que un elefante

I think i got it right but why use unas and not las

Answer 1

You "almost" got this one.

Unas casas con más GRANDES que un elefante.

The adjective "large" modifies the noun "houses" so must be feminine and plural also.

Good question about "unas" versus "las."

INDEFINITE article "a, an" = un, una, unos, unas

DEFINITE article "the" = el, la, los, las

Here you need to decide then if you want "some" houses or "the" houses.

Sra