1.

(1 - pnorm(30,28.8,3.1)) / (1 - pnorm(25,28.8,3.1))

2.  

mean(pe$age)

3.

(3.22)

4.

qgamma(0.90,5,0.01)

5.

f <- function(nreps)

{
   tmp <- replicate(nreps,sum(runif(50,-0.5,0.5)))
   mean(tmp > 2.0)
}

f(10000)