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Answer: We are 95% confident that the mean SPF level of sunscreen used by all Cal Poly students is between 29.0813 and 40.0187.
Step-by-step explanation:
Given : Significance level :
Sample size : n= 52 , which is a large sample (n>30), so we use z-test.
By using z-value table,
Critical value:
Sample mean :
Standard deviation :
The confidence interval for population means is given by :-
i.e.
Now, the 95% confidence interval for the ppopulation mean = . (29.0813, 40.0187)
Hence, We are 95% confident that the mean SPF level of sunscreen used by all Cal Poly students is between 29.0813 and 40.0187.