Discipline in which working out with equals should get results (10)

I believe the answer is:

arithmetic

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

'discipline' is the definition.
(I know that arithmetic is a type of pure mathematics)

I don't understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for arithmetic that I've seen before include "Branch of maths" , "School subject" , "manipulation of figures" , "Branch of mathematics" , "summing up maybe" .)

I've seen this clue in The Telegraph.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.