quick at
I need to translate
Ahi estuviste rapida
Muy lista
It's said if someone gives you a quick answer to a difficult question.
My attempts. You were quick at that
Very clever from you

Thanks

Question

quick at
I need to translate 
Ahi estuviste rapida
Muy lista
It's said if someone gives you a quick answer to a difficult question.
My attempts.  You were quick at that
 Very clever from you

Thanks

Answer

I would recommend "That was quick" if you are speaking to the person and don't know them well enough to too friendly. If you want to be very informal, you could say, "you're a speed demon", or "you're a brain box", or even "you're on fire".