Crossword Genius

Question of putting two and two together? (3)

Ross

I believe the answer is:

sum

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

'question' is the definition.
The answer and definition can be both to do with communicating as well as being verbs in their base form.
Maybe there's an association between them I don't understand?

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for sum that I've seen before include "Total, add" , "All one has" , "Amount, aggregate" , "Add together" , "An additional problem" .)

I've seen this clue in the Evening Standard.
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