To find the mean, we have to add all the numbers to then divide that sum by the total number of elements.
Chart A.
Let's sum each row.
8 + 8 + 9 = 25
1 + 2 + 2 + 4 + 5 + 5 + 8 = 27
1 + 1 + 3 + 6 + 7 = 18
0 + 3 + 4 + 4 + 5 = 16
The mean of chart A is 21.5.
Chart B.
1 + 1 + 2 + 4 + 7 + 7 = 22
2 + 3 + 3 + 6 + 8 + 9 = 31
3 + 5 + 5 + 6 + 7 + 8 + 9 = 43
Then, we subtract
Hence, the difference between the means is 2.5.