n = 11;
x=2:12;
p = [1,2,3,4,5,6,5,4,3,2,1]/36;
sum ( p )
ave = 0.0;
for i = 1 : n
  ave = ave + p(i) * x(i);
end
ave
var = 0;
for i = 1 : n
  var = var + p(i) * ( x(i) - ave )^2;
end
var