1. Mean deviation of mean for Grouped data:
Discrete frequency distribution :
Let the given data consist of k distinct values `x_1,x_2,...,x_k` with frequencies `f_1,f_2,...,f_k` respectively.
This is called discrete frequency distribution

Mean deviation of mean is defined by the formula

`delta bar x = (sum f_i*|x_i - bar x|)/n`
where
sum of all frequencies `=n=sum f_i`
mean `=bar x = (sum f_i*x_i)/n`
`|x_i - bar x|` is absolute difference between `x_i` and mean `bar x`

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2. Mean deviation of median :
Mean deviation of median `delta M = (sum f_i*|x_i - M|)/n`

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3. Mean deviation of mode :
Mean deviation of mode `delta Z = (sum f_i*|x_i - Z|)/n`

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