Question

In a survey, 30 people were asked how much they spent on their child's last birthday gift. The results were roughly bell-shaped with a mean of $39 and standard deviation of $10. Construct a confidence interval at a 80% confidence level.

Give your answers to one decimal place.

Answer 1

We have given that,          
          
Sample mean =$39  
Sample standard deviation =$10
Sample size =30  
Level of significance=1-0.80=0.2  
Degree of freedom =29  
          
t critical value is (by using t table)=   1.311  
          
Confidence interval formula is           


=(36.6,41.4)      
          
          
Lower confidence limit=$36.6
          
Upper confidence limit=$41.4