Question

A medical center wants to determine the mean duration of human pregnancy. A sample of 49 pregnancies showed a sample mean = 282 days with sample standard deviation s = 12 days. Create a confidence interval at 90% confidence for the population mean.

Answer 1

We have given that,          
          
Sample mean =282 days  
Sample standard deviation =12 days
Sample size =49  
Level of significance=   1-0.90=0.1  
Degree of freedom =48  
          
t critical value is (by using t table)=   1.677  
          
Confidence interval formula is

=(279.12,284.88)          
          
          
          
Lower confidence limit=   279.12  
          
Upper confidence limit=   284.88