How am I supposed to know that it is plural feminin?
You don't know, but "Ei arată deștepți" is also accepted :)
Is that smart as in clever, or as in well-dressed?
If I translate correctly dexonline's definition, deștepte means "which understands easily and precisely what he reads, hears, sees; quick-witted, intelligent".
Thank you :-)
why no!? ei urata destepti
It should be accepted, report it. (unless it was rejected because of the typo)
Is "ei arată isteți" correct?
In English THEY is used for feminine and masculine, you shoud accept my answer.
According to Mapta15, "Ei arată deștepți" is accepted. Maybe what you wrote was refused for some other reason.