
Concept explainers
For Exercises 9 through 15, perform these steps. Assume that all variables are normally or approximately
a. State the hypotheses.
b. Find the critical value for each F test.
c. Complete the summary table and find the test value.
d. Make the decision.
e. Summarize the results. (Draw a graph of the cell means if necessary.)
10. Increasing Plant Growth A gardening company is testing new ways to improve plant growth. Twelve plants are randomly selected and exposed to a combination of two factors, a “Grow-light” in two different strengths and a plant food supplement with different mineral supplements. After a number of days, the plants are measured for growth, and the results (in inches) are put into the appropriate boxes.
Grow-light 1 | Grow-light 2 | |
Plant food A | 9.2, 9.4, 8.9 | 8.5, 9.2, 8.9 |
Plant food B | 7.1, 7.2, 8.5 | 5.5, 5.8, 7.6 |
Can an interaction between the two factors be concluded? Is there a difference in mean growth with respect to light? With respect to plant food? Use a = 0.05.

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