This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Biostatistics, Subject name: Social & Preventive Medicine
What is the probability that confounding factor fall to the right of 95%- 
Select and explain. 
A. 1 in 5, B. 1 in 10, C. 1 in 20, D. 1 in 40
D: 1 in 40
Answer: D: 1 in 40 
Explanation: Ref:Parks 23rd edition pg 849. 1SD : confidence limit = 68% 2SD : confidence limit = 95% 3SD : confidence limit = 99.7% Here 5% values remains and falls to the right and left altogether . So, 2.5% lies to the right and 2.5 to the left . 2.5/100= 1/40