Make sums make sense? (3,2)
I believe the answer is:
add up
'make sense?' is the definition.
('add up' can be a synonym of 'make sense')
I can't explain the remainder of the clue.
Can you help me to learn more?
(Other definitions for add up that I've seen before include "Make sense; count" , "Aggregate, get total" , "Put together (numbers)" , "Ring true" , "Seem consistent or reasonable - arithmetically?" .)