grid=seq(1,16,0.1); xbar.mu=7; pop.dens=0.6*dnorm(grid,5,1)+0.4*dnorm(grid,10,2)
n=2 # n IS THE SAMPLE SIZE GOING INTO EACH SAMPLE MEAN, TRY n=1,2,3,5,10,20 
m=10000; xbars=rep(0,m) # m IS NUMBER OF SAMPLE MEANS GENERATED; JUST LEAVE THIS AT 10000
for(j in 1:m){b=rbinom(n,1,0.6); d=rnorm(n,5,1)*b+rnorm(n,10,2)*(1-b); xbars[j]=mean(d)}
xbar.var=8.2/n; xbar.std=sqrt(xbar.var)
xbar.dens=dnorm(grid,xbar.mu,xbar.std)
hist(xbars,freq=FALSE,xlim=c(1,16)); lines(grid,pop.dens); lines(grid,xbar.dens,lty=3)