Question

A random sample of 16 pharmacy customers showed the waiting times below (in minutes). Also, the sample is from a normal population. Note that σ is unknown. 21 22 22 17 21 17 23 20 20 24 9 22 16 21 22 21 The sample mean is 19.875 and the sample standard deviation is 3.65. Which of the following represents the 80 percent confidence interval for µ?

Select one:

a. [13.75, 25.25]

b. [18.65, 21.10]

c. [19.55, 20.425]

d. [18.8, 21.2]

Answer 1

Option b) is correct.

b. [18.65, 21.10]

We have given that,          
          
Sample mean =   19.875  
Sample standard deviation =   3.65
Sample size =   16  
Level of significance=   1-0.80=0.2  
Degree of freedom =   15  
          
t critical value is (by using t table)=   1.341
          
Confidence interval formula is   

=(18.65,21.10)      
          
          
          
Lower confidence limit=   18.65  
          
Upper confidence limit=   21.10