We know, Sum of deviation of variate from their A.M. is always zero that is $\sum(x_i- \mu)$ where $x_i$ are all the elements and $\mu$ is the arithmetic mean.
Also mean deviation is the mean of the variates around a given quantity. If it is asked to find the mean deviation around the mean, then it should be zero, right? This is where I am unable to understand it. Any help will be appreciated.