Quick test noted for giving maximum return? (4)

I believe the answer is:

exam

I'm a little stuck... Click here to teach me more about this clue!

'quick test' is the definition.
'exam' can be an answer for 'test' (I've seen this before). I am unsure of the 'quick' bit.

I don't understand the rest of the clue.

Can you help me to learn more?

(Other definitions for exam that I've seen before include "Written test" , "Test (abbr)" , "In brief, a test as in school" , "Formal knowledge test" , "End-of-course assessment" .)

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