Final answer:
To find the upper-tail critical value of the test statistic in a contingency table, calculate the degrees of freedom and use a chi-square critical values table.
Step-by-step explanation:
To determine the upper-tail critical value of the test statistic in a contingency table, we first need to find the degrees of freedom (df). The formula to calculate df is df = (number of rows - 1)(number of columns - 1). In the given problem statement for part (a), r = 4 and c = 5, so df = (4 - 1)(5 - 1) = 3 * 4 = 12.
Next, we can use a chi-square critical values table to find the upper-tail critical value for a given significance level. Since a = 0.05, we look for the critical value in the row corresponding to 0.05 and the column corresponding to df = 12.
From the table, we find that the critical value is approximately 21.026, rounded to three decimal places.