Answer: 1.303639
Step-by-step explanation:
The t-score for a level of confidence [tex](1-\alpha)[/tex] is given by :_
[tex]t_{(df,\alpha/2)}[/tex], where df is the degree of freedom and [tex]\alpha[/tex] is the significance level.
Given : Level of significance : [tex]1-\alpha:0.80[/tex]
Then , significance level : [tex]\alpha: 1-0.80=0.20[/tex]
Sample size : [tex]n=40[/tex]
Then , the degree of freedom for t-distribution: [tex]df=n-1=40-1=39[/tex]
Using the normal t-distribution table, we have
[tex]t_{(df,\alpha/2)}=t_{39,0.10}=1.303639[/tex]
Thus, the t-score should be used to find the 80% confidence interval for the population mean =1.303639
