8. Six samples of each of four types of cereal grain grown in a certain region were analyzed to determine thiamin content, resulting in the following data (mg/g):

Wheat 5.2 4.5 6.0 6.1 6.7 5.8 Barley 6.5 8.0 6.1 7.5 5.9 5.6 Maize 5.8 4.7 6.4 4.9 6.0 5.2 Oats 8.3 6.1 7.8 7.0 5.5 7.2

a. Check the ANOVA assumptions with a normal probability plot and a test for equal variances.

b. Test to see if at least two of the grains differ with respect to true average thiamin content. Use an a  .05 test based on the P-value method.