10. Use cs=read.table(”Concr.Strength.1s.Data.txt”, header=T); x=cs$Str to store the data set2 consisting of 28-day compressive-strength measurements of concrete cylinders using water/cement ratio 0.4 into the R object x.

(a) Use the commands given in Section 3.5.2 to produce a normal Q-Q plot for the data. Comment on the appropriateness of the normal model for this data set.

(b) Using X and S2 as estimators of the model parameters of N(μ, σ2), give model-based estimates of P(44 <

X ≤ 46), the population median, and the 75th percentile.

(c) Give the empirical, or model-free, estimates of the above population quantities. (Hint. The R command sum(44

For the sample percentiles see the R commands given in (1.7.2).)

(d) Which of the two types of estimates for the above population quantities would you prefer and why?