Crossword Genius

Assumed total? (3)

Ross

I believe the answer is:

sum

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

'total?' is the definition.
(I know that total can be written as sum)

'assumed' is the wordplay.
'SUM' is hidden in amongst the letters.
But, I am uncertain how the hidden word is indicated.

Can you help me to learn more?

(Other definitions for sum that I've seen before include "Amount, aggregate" , "Whole" , "Total; problem" , "See 25" , "maths problem" .)

I've seen this clue in the Evening Standard.
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