replacing the parameters

path = 'D:\images\';
imagelist = dir(strcat(path,'*.jpg'));

idk = 0;
for x = 1 : 8  
      for y = 1 : 10
          idk = idk + 1;
          I = imread(fullfile(path,imagelist(idk).name));  
          mean10(y) = mean(I(:));
      end
      mean8(x) = mean(mean10(:));   
  end

I have to substitute R=6/8,and p=6/28 in place of mean10(y),such that i get values of R and P for every image

in place of mean 8 in need the average (each 10 values of R and P )

i tried but not getting values for individual image ,please help