Please see the above image, the average of cr1 for A, B, & C is 352.67 and for cr2, it is 285.33.
Now, if I divide cr2 by cr1 and take the average of A, B, & C, I get 0.92, but a division of the two averages shows up as 0.81.
How do I get 0.81 to be 0.92 instead, by using the average values.
Basically, I am creating a report, where A, B, & C are the values of individual stock and the average price of that is the portfolio's value, then I am calculating the relative change in value, but it is coming out wrong.
As has been remarked in the comments, the ratio of averages is not the average of the ratios.
More to the point, if all you are given are the averages of the two data sets, you can not calculate the average of the ratios. To see this suppose the two data sets are permutations of each other. Then they have the same average and the ratios might have average $1$ (if the permutation is trivial, say) but might not. $\{1,3\}$ and $\{3,1\}$ both have average $2$ but their ratios $\{\frac 13, 3\}$ have average $\frac 53$.