Arithmetical problem (3)
I believe the answer is:
sum
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">arithmetical problem</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for sum that I've seen before include "Arithmetic calculation" , "An additional problem" , "Aggregate, total" , "Amount, aggregate" , "Quantity obtained by addition" .)