Twenty per cent of Beethoven's work, maybe? (5)
I believe the answer is:
fifth
'twenty' is the definition.
The definition and answer can be both quantities as well as being singular nouns.
Perhaps there's a link between them I don't understand?
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for fifth that I've seen before include "taken by Americans in self-defence" , "Musical interval" , "Fraction" , "20 per cent" , "Twenty percent" .)