# set sample size and number of samples
set.seed(23456789)
n <- 11
reps <- 1000

# perform random sampling
samples <- replicate(reps, runif(n)) # 11 x 1000 sample matrix

# compute sample means
sample_mean <- colMeans(samples)

# check that 'sample_mean' is a vector
is.vector(sample_mean) 

(mean(sample_mean))
(sd(sample_mean))
(var(sample_mean))

hist(sample_mean, breaks=40, prob=T, main=paste( "samples of size 11" ),col="steelblue")
par(new=T)
plot(density(sample_mean), xlab="", axes=F, main="", col="black")

library(openxlsx)
samples.dat<-data.frame(samples)
write.xlsx(samples.dat, "C:/Users/user/Desktop/b1-ch5-3-new.xlsx", colNames=T, asTable=F)