Competent at arithmetic (8)
I believe the answer is:
numerate
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">competent at arithmetic</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for numerate that I've seen before include "Good at arithmetic" , "Having a good knowledge of maths" , "Well versed in maths" , "Able to do arithmetic" , "Arithmetically competent" .)