The people in a country are partitioned into clans. In order to estimate the average size of a clan, a survey is conducted where $1000$ randomly selected people are asked to state the size of the clan to which they belong. How does one compute an estimate average clan size from the data collected?
Source: puzzledquant.com
My approach: I am thinking of using $E[X]$=$E[E[X|N]]$ where $X$ is size and $N$ is the clan I am currently in. But I am unsure how to proceed from here. Help.