Mean deviation (Mean deviation of mean):
Mean of positive differenes of observations of data from their mean is called mean deviation.
It is denoted by `delta bar x` and read as delta x bar.
This is also called Mean deviation of mean

Mean deviation of Mean `delta bar x = (sum |x - bar x|)/n`

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Mean deviation of median :
Mean of positive differenes of observations of data from their median is called mean deviation of median.
It is denoted by `delta M`

Mean deviation of Median `delta M = (sum|x - M|)/n`

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Mean deviation of mode :
Mean of positive differenes of observations of data from their mode is called mean deviation of mode.
It is denoted by `delta Z`

Mean deviation of Mode `delta Z = (sum|x - Z|)/n`

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