"Είσαι γρήγορος."

Translation: You are fast.

[SandraGerd1]

the female version - would it be γρηγορα?

[troll1995]

It's γρήγορη. Η γυναίκα είναι γρήγορη=The woman is fast. Γρήγορα is the neuter plural nominative and the adverb. Τα παιδιά είναι γρήγορα=The kids are fast. Τρέχει γρήγορα=He/she/it runs fast.

[Serguei413435]

In γρήγορος it sounds like with an accent on omikron: γρηγόρος

[MDR215875]

On slow speed sounded like 'verygoros' made no sense but sounded like thar

[G.Georgopoulos]

Sounds ok to me (web version).

[MDR215875]

Am I suprised

[Frank162000]

Isn't 'Are you fast' also acceptable?

[mizinamo]

Isn't 'Are you fast' also acceptable?

No. Your sentence is a question; Duo's sentence is a statement. (Note the period "." at the end rather than a question mark ";".)

[Frank162000]

Right you are. In the written context we rely on the visual cues of punctuation. But if this is spoken with an upward inflection at the end, would it not be a question? The only difference would be the order of the words, 'Are you fast?' vs 'You are fast?'