reverse engineering random number generating

hi
I can generate 100 random numbers between 1 and 5 [as =randbetween(1,5) or else] and calculate ∑x^2/∑x [x=random numbers] on a cell. My question is: how can I do it in reverse? In other words, suppose A1:A100 my potential random numbers, and B1 my formula ∑x^2/∑x. How can I generate A1:A100 based on B1=4 [for instance], whether exactly or approximately.
regards
tourman