This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Disease Causation, Measurements, Milestones, Subject name: Social & Preventive Medicine
In a population of 5000, number of new cases of TB is 500; old cases in the same population are 150. What is the prevalence of TB? 
Select and explain. 
A. 9%, B. 12%, C. 13%, D. 18%
C: 13%
Answer: C: 13% 
Explanation: Prevalence = total number of cases / total population x 100 = (650/5000) x100 =13%