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 (which is in a very sunny part of the U.S.) exceeds this value, on average?
a. Identify the variable of interest and whether the variable is categorical or quantitative.
b. Describe the author’s parameter of interest and assign an appropriate symbol to denote it.
c. Write the appropriate hypotheses using symbols. To collect data, the author surveyed students in her Introductory Statistics course and found that in a sample of 48 students the average SPF was 35.29 and the standard deviation of SPF was 17.19.
d. Assign appropriate symbols to the numbers 48, 35.29, and 17.19.

e. Do the data come from a random sample? Explain.
f. Do you think the students in the Introductory Statistics course are representative of all students at this school, with regard to SPF of their sunscreens? Why or why not?
g. Describe a population for which this sample is surely not representative, with regard to SPF of sunscreens used.