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The following is the cumulative frequency distribution (of less than type) of \(1000\) persons each of age \(20\) years and above. Determine the mean age.
 
Age below (in years) Number of persons
\(30\) \(100\)
\(40\) \(220\)
\(50\) \(350\)
\(60\) \(750\)
\(70\) \(950\)
\(80\) \(1000\)
 
Answer:  
 
The mean age of \(1000\) persons is .
 
[Note: Enter the answer in to whole number.]