Mean = (21 + 22 + 24 + 26 + 27 + 28 + 20 + 30) / 8 = 218 / 8 = 27.25
Calculate the absolute difference between each value and the mean:
|21 - 27.25| = 6.25
|22 - 27.25| = 5.25
|24 - 27.25| = 3.25
|26 - 27.25| = 1.25
|27 - 27.25| = 0.25
|28 - 27.25| = 0.75
|20 - 27.25| = 7.25
|30 - 27.25| = 2.75
Find the average of these absolute differences:
MAD = (6.25 + 5.25 + 3.25 + 1.25 + 0.25 + 0.75 + 7.25 + 2.75) / 8
= 26.75 / 8
= 3.34375
Rounded to the nearest whole number, the mean absolute deviation (MAD) of the given data set (21, 22, 24, 26, 27, 28, 20, 30) is 3.