Refer to Exercise 11.34. Use the Empirical Rule to create an interval that estimates the textbook expenses of 95% of the individual students at the university (not the mean).
Exercise 11.34
A randomly selected sample of n = 12 students at a university is asked, “How much did you spend for textbooks this semester?” The responses, in dollars, are
200, 175, 450, 300, 350, 250, 150, 200, 320, 370, 404, 250
Computer output with a 95% confidence interval for the population mean follows:
a. Draw either a dotplot or a boxplot of the data. Briefly discuss whether or not the necessary conditions for doing a confidence interval for the population mean are present.
b. The standard error of the mean given in the output is 27.7 (under “SE Mean”). Verify this value by giving the correct formula and substituting appropriate values into this formula.
c. What are the degrees of freedom for the t* multiplier? What is the value of the t * multiplier for the given confidence interval?
d. Write a sentence that interprets the confidence interval. Be specific about the population that is being described.
e. Calculate a 90% confidence interval for the population mean.