This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Social & Preventive Medicine
Study the following table of population in a district and the average population served per doctor. Calculate the harmonic mean: AREA POPULATION SERVED PER DOCTOR POPULATION NUMBER OF DOCTORS RURAL 1000 50000 50 URBAN 500 50000 100 TOTAL 100000 150 
Select and explain. 
A. 500, B. 567, C. 667, D. 750
C: 667
Answer: C: 667 
Explanation: Calculation of harmonic mean is as follows: (50000+50000)/(50000/100+50000/50)=667 Ref : Medical biostatistics, 1st edition pg: 118