\[\large Mean\;Deviation\;from\;Mean=\frac{\sum \left |X-\overline{X}\right|}{N}\]

\[\large Mean\;Deviation\;from\;Median=\frac{\sum \left |X-M\right|}{N}\]

M = Median

For frequency distribution, the mean deviation is given by:

\[\large M.D=\frac{\sum f \left | X-\overline{X} \right |}{\sum f}\]

When the mean deviation is calculated about the median, the formula becomes:

\[\large M.D (about\;median)=\frac{\sum f\left | X-Median \right |}{\sum f}\]

The mean deviation about the mode is:

\[\large M.D (about\;mode)=\frac{\sum f\left | X-Mode\right |}{\sum f}\]

For a population data, the mean deviation about the population mean

\[\large M.D=\frac{\sum f\left | X-\mu \right |}{\sum f}\]