Crossword Genius

It often involves unknown quantities (7)

Ross

I believe the answer is:

algebra

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'it often involves unknown quantities' is the definition.
The definition suggests a singular noun which matches the answer.

This is the entire clue.

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(Other definitions for algebra that I've seen before include "Branch of generalised arithmetic" , "Calculation by symbols" , "Symbolic mathematics" , "Maths with letters representing numbers" , "Branch of maths using letters and symbols" .)

I've seen this clue in The Globe and Mail.
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