pausa <- function() { cat ("\n >> press Enter to continue\n"); scan() }

outcomes <- as.vector(outer(1:6,1:6))
N = 50
n = 20000
sx = rep(0, n)
for(ns in 1:N) {
  xi <- runif(n, 0, 0.25) + sample(c(0,1), n, rep=TRUE)*0.5
  sx = sx + xi
  hist(sx, nc=200, col='cyan', xlab='Sum X', freq=FALSE, 
       main=sprintf("ns = %d; mean = %.1f, std = %.1f ",
                    ns, mean(sx), sd(sx)))
  if(ns>3) plot(function(x) dnorm(x, mean(sx), sd(sx)), add=TRUE, lwd=3,
                xlim=c(mean(sx)-4*sd(sx), mean(sx)+4*sd(sx)), col='magenta')
  pausa()
}