The report “Motorcycle Helmet Use in 2005—Overall Results” (NHTSA August 2005) included observations made on the helmet use of 1700 motorcyclists across the country. The data is summarized in the accompanying table. (A “noncompliant helmet” failed to meet U.S. Department of Transportation safety guidelines.)

a. What is the variable in this example? What are the possible values of that variable?
b. Construct the relative frequency distribution of this variable.
c. What proportion of observed motorcyclists wore some kind of helmet?
d. Construct an appropriate graph for this data.

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Category No helmet Noncompliant helmet Compliant helmet Total Frequency 731 153 816 1700