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: Dental
In a class, the mean weight of 4 students is 90 kg and standard deviation is 30, then 95% confidence interval would be accordingly: 
Select and explain. 
A. 60-80, B. 30-150, C. 60-120, D. 70-110
B: 30-150
Answer: B: 30-150 
Explanation: Here, Mean = 90 ; Standard deviation = 30
95% confidence interval = Mean +/- 2 S.D
Hence, 90+ (2x30) = 90+60 = 150
             90- (2x30) = 90-60 = 30