Answer:
[tex]CI=\{2.5053,3.2147\}[/tex]
Step-by-step explanation:
Assuming the conditions for constructing a t-confidence interval are true, we use the formula [tex]\displaystyle CI=\bar{x}\pm t^*\biggr(\frac{s}{\sqrt{n}}\biggr)[/tex] where our sample mean is [tex]\bar{x}=2.86[/tex], our sample standard deviation is [tex]s=0.78[/tex], our sample size is [tex]n=15[/tex], and a 90% confidence level is equivalent to a critical value of [tex]t^*=1.7613[/tex],
[tex]\displaystyle CI=\bar{x}\pm z^*\biggr(\frac{s}{\sqrt{n}}\biggr)\\\\CI=2.86\pm 1.761\biggr(\frac{0.78}{\sqrt{15}}\biggr)\\\\CI=2.86\pm0.3547\\\\CI=\{2.5053,3.2147\}[/tex]
Hence, we are 90% confident that the true population mean of a student's grade point average is between 2.5053 and 3.2147
