Can someone explain mathematically why the difference of the sum of the
average of row two and three (Range D2:D3) as shown in cell E3 is different
than the average of each individual difference in range A4:C4 as shown in
cell E4.
It is not obvious to me.

test 1 test 2 test 3 Average Diff
10 5 10 8,33
6 1 2 3 -64,00 %
-40,00 % -80,00 % -80,00 % -66,67 %

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Regards
Tommy