Answer:
3 or 3.0
Explanation:
the mean absolute deviation is the mean value of the sum of all differences (absolute values) of the data points to the mean value of the list of data points.
to get that we need to find the general mean value first.
that is the sum of all data points divided by the number of data points :
(12+10+8+15+15+18) / 6 = 78/6 = 13
the mean absolute deviation is now the sum of the differences of the data points to 13, and then again divided by 6 :
(13-12 + 13-10 + 13-8 + 15-13 + 15-13 + 18-13) / 6 =
= (1 + 3 + 5 + 2 + 2 + 5) / 6 = 18/6 = 3