The following table shows data for grades usually achieved in school and how often the respondent puts on sunscreen when going out in the sun for more than 1 hour. Respondents are 12th-grade participants in the 2003 Youth Risk Behavior Surveillance System survey. The survey, sponsored by the U.S. Centers for Disease Control and Prevention, is a national survey of high school students. (Raw data are in the YouthRisk03 dataset on the companion website.)

a. Among students who usually get A's and B's in school, what percentage never or rarely uses sunscreen when going out in the sun for more than one hour? Explain whether this value is a row percentage or a column percentage.

b. Among students who sometimes wear sunscreen, what percentage usually gets C's in school? Explain whether this value is a row percentage or a column percentage.

c. What percentage of the overall sample usually gets A's and B's in school and also uses sunscreen always or most times when going out in the sun for more than one hour?

d. Determine a complete table of row percentages.

e. Briefly explain whether the percentages found in part (d) indicate that there is a relationship between grades usually achieved and frequency of sunscreen use.