Refer to Fig. 7.6 on page 295.
a. Why are the four graphs in Fig. 7.6(a) all centered at the same place?
b. Why does the spread of the graphs diminish with increasing sample size? How does this result affect the sampling error when you estimate a population mean, μ, by a sample mean, x-bar?
c. Why are the graphs in Fig. 7.6(a) bell shaped?
d. Why do the graphs in Figs. 7.6(b) and (c) become bell shaped as the sample size increases?