We know that mean of the observation is given by ratio of sum of observation to number of observation,

So, Mean $=\frac{1+3+4+7+11+18+29+47+78}{9}=\frac{198}{9}=22$

Now the mean deviation from the mean of the discrete data $1,3,4,7,11,18,29,47,78$ will be,

$M.D=\frac{\left|1-22\right|+\left|3-22\right|+\left|4-22\right|+\left|7-22\right|+\left|11-22\right|+\left|18-22\right|+\left|29-22\right|+\left|47-22\right|+\left|78-22\right|}{9}$

$M.D=\frac{21+19+18+15+11+4+7+25+56}{9}=\frac{176}{9}$