The standard deviation of test scores on a certain achievement test is 11.3. if a randomsample of 81 students had a sample mean score of 74.6, find a 90 percent confidence interval estimatefor the average score of all students.

(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)

26?

step-by-step explanation: