Answer: (72.535, 76.665)
Step-by-step explanation:
The confidence interval for population mean is given by :-
, where = population standard deviation.
n= Sample size
= sample mean.
= Critical z-value (two-tailed)
Given :
n= 81
The critical values for 90% confidence interval :
Now, the confidence interval for population mean would be :
Hence, a 90 percent confidence interval estimatefor the average score of all students. : (72.535, 76.665)