Mean of the given data is
The deviations of the respective observations from the mean
x, i.e.
xi−x are
2−6,9−6,9−6,3−6,6−6,9−6,4−6
⇒−4,3,3,−3,0,3,−2
The absolute values of the deviations, i.e.
|xi−x| are 4,3,3,3,0,3,2
The required mean deviation about the mean is
MD(x)= = ==2.57