If you have each matrix stored in a separate variable, you can do
Atotal = A1 + A2 + A3; % Sum of logical matrices is a numeric matrix
Atotal = (Atotal/3 > 0.75) ; % Create a logical matrix where each entry is true if >75%
% of matrices have an entry that is true
If you have many matrices, it may be easier to store them all in a 3-D array of size 125-by-125-by-numMatrices. Then, the computation you describe can be done like this:
Atotal = sum(A, 3);
Atotal = (Atotal/size(A, 3) > 0.75);
