Environmental scientists performed a two-factor experiment in which the response variable was the amount of an herbicide absorbed by a certain type of plant. The factors were the concentration of the herbicide and the ratio of the delivery rates of iron and water. The following MINITAB output presents the results.

a. Test the null hypothesis of no interaction between concentration and delivery ratio.

b. If the null hypothesis of no interaction is not rejected, test the hypothesis that there is no main effect of concentration. Interpret the result.

c. If the null hypothesis of no interaction is not rejected, test the hypothesis that there is no main effect of delivery ratio. Interpret the result.

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Analysis of Variance for Sorption Source DF SS MS F P Concentration 2 0.3793 0.1897 3.873 0.040 Delivery Ratio 2 7.3400 3.6700 74.95 0.000 Interaction 4 3.4447 0.8612 17.59 0.000 Error 18 0.8814 0.0490 Total 26 12.045