Are the data Normal? Soil penetrability. Table 2.5 (page 65) gives data on the penetrability of soil at each of three levels of compression. We might expect the penetrability of specimens of the same soil at the same level of compression to follow a Normal distribution. Make stemplots of the data for loose and for intermediate compression. Does either sample seem roughly Normal? Does either appear distinctly non-Normal? If so, what kind of departure from Normality does your stemplot show?

The Normal Curve applet allows you to do Normal calculations quickly. It is somewhat limited by the number of pixels available for use, so that it can’t hit every value exactly.
In the exercises below, use the closest available values. In each case, make a sketch of the curve from the applet marked with the values you used to answer the questions.