The mean of the combined group can be calculated as follows:
Calculate the total sum of test scores of both classes:
Class 1: 36 students * 73.1 mean = 2631.6
Class 2: 28 students * 67.4 mean = 1888.32
Total: 2631.6 + 1888.32 = 4519.92
Calculate the total number of students:
Total students = 36 + 28 = 64
Divide the total sum of test scores by the number of students to find the mean:
Mean = 4519.92 / 64 = 70.9375.
Therefore, the mean of the combined group of 64 students is 70.9375.