This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Screening, Subject name: Social & Preventive Medicine
A population of 1000 people in whom the prevalence of disease XYZ is 50%. ABC screening test was used to screen disease which has specificity and sensitivity of 50 %. What is positive predictive value of screening test ABC. 
Select and explain. 
A. 50%, B. 25%, C. 75%, D. 10%
A: 50%
Answer: A: 50% 
Explanation: Total Population = 1000 Prevalence = 50% People have Disease = 500 Not have Disease = 500 Method 1 Test Disease [?] Th [?] A TP ? B FP ? Th C FN ? D TN ? 500 (given) 500 (given) 1000 (given) Test Disease [?] Th [?] A 250 B 250 Th C 250 D 250 Method 2 ( Baye's Theorum)