Matrix multiplication

Run and explain the following:

A = randn(3000);

tic
for k = 1:10
    C = A' * A;
end
toc

tic
for k = 1:10
    C = A * A';
end
toc

tic
for k = 1:10
    C = A * A;
end
toc

and the following

A = rand(3000); B = rand(3000); tic for k = 1:10 C = A * B; end toc A = single(A); B = single(B); tic for k = 1:10 C = A * B; end toc