Most dermatologists recommend using sunscreens that have a Sun Protection Factor (SPF) of at least 30. One of the authors wanted to find out whether the SPF of sunscreens used by students at her school exceeds this value on average? To collect data, the author surveyed students in her introductory statistics course and found that in a sample of 48 students the mean SPF was 35.29 and the standard deviation of SPF was 17.19. Th e data were not strongly skewed.
a. Identify the observational units for this study.
b. Identify the variable of interest and whether it is categorical or quantitative.
c. Use the Theory-Based Inference applet to find and report the 95% confidence interval for the parameter of interest and provide an interpretation of the interval, in the context of the study.

d. Assuming she has a representative sample, based on the confidence interval, is the average SPF of sunscreens of the students at the author’s school higher than 30? How are you deciding?
e. Are the conditions required for the validity of the above results satisfied? State the condition(s) and explain your reasoning.