12.6 Determining the critical value of F. For each of the following situations, state how large the F statistic needs to be for rejection of the null hypothesis at the 0.05 level. (a) Compare 3 groups with 5 observations per group. (b) Compare 4 groups with 4 observations per group. (c) Compare 4 groups with 8 observations per group. (d) Summarize what you have learned about F distributions from this exercise.