We decided to pay the movers [twenty percent extra/extra twenty percent] for the great job.

Which is correct?

Thanks in advance!
I think extra should modify here. .. extra twenty percent.
Mm ... I would add "an":
... to pay the movers an extra twenty percent for ...

Wait for a native, though!
Emotion: smile
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Yes an an is needed here.
Thank you, guys. Yes, I agree that 'an' is needed here. I'd like to hear from a native as I still think twenty percent extra could be correct as well. For example, I'm hundred percent sure that ... hundred percent here is used as adjective.
Yes, there is nothing wrong with twenty percent but using it with extra needs careful grammar. Emotion: smile
Students: We have free audio pronunciation exercises.

I gave all the children pencils, but I gave Mary five extra.

I gave all the children pencils, but I gave Mary an extra five.

Both are OK. Perhaps #1 sounds a little more like informal speech.