An ANOVA is used to study the effect of seam differences on variability in the sulfur content of coal. Seams and samples from seams are taken at random.

a. Do differences among seams contribute significantly to the variability in the sulfur content of coal?

b. What percentage of the variability in the sulfur content of coal is attributable to seam differences?

c. Would you advise coal producers in search of low-sulfur coal to seek low-sulfur seams or to seek other factors that might affect variability? Justify your answer on the basis of the above analyses.