This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Epidemiology, Subject name: Social & Preventive Medicine
In a population of 5000, incidence of disease is 100 in 1 year. Duration of disease studied for is 2 years. Calculate prevalence 
Select and explain. 
A. 20\/1000, B. 40\/1000, C. 80\/1000, D. 400\/1000
B: 40\/1000
Answer: B: 40\/1000 
Explanation: Ref: Parks 23rd edition pg 61. Prevalence = Incidence x Duration = (100/5000) x 2 = (20/1000) x 2 = 40/1000