Crime that I cracked? It's not all adding up (10)

I believe the answer is:

arithmetic

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'crime that i cracked? it's not all adding up' is the definition.
Although both the answer and definition are singular nouns, I don't see how one could define the other.

'crime that i cracked?' is the wordplay.
'cracked?' is an anagram indicator.
'crime'+'that'+'i'='crimethati'
'crimethati' anagrammed gives 'ARITHMETIC'.

Can you help me to learn more?

(Other definitions for arithmetic that I've seen before include "kind of mean" , "Branch of maths" , "Numerical calculations" , "Calculating" , "summing up maybe" .)

I've seen this clue in The Telegraph.

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