n = [5 10 20 30];
k=500;
mu = 3;sigma=0.16;
for i = 1:4
  X = exp(normrnd(mu,sigma,n(i),k));
  m = mean(X);
  subplot(2,2,i);
  hist(m);
  axis([16 26 0 150]);
  str = sprintf('n= %d',n(i));
  title(str);
end
