91Ó°ÊÓ

You are preparing to study the television-viewing habits of high school students. Describe two categorical variables and two quantitative variables that you might record for each student.

Students in a college statistics class responded to a survey designed by their teacher. One of the survey questions was "How much sleep did you get last night?" Here are the data (in hours): $$ \begin{array}{lrrrrrrrrrrrr} \hline 9 & 6 & 8 & 6 & 8 & 8 & 6 & 6.5 & 6 & 7 & 9 & 4 & 3 & 4 \\ 5 & 6 & 11 & 6 & 3 & 6 & 6 & 10 & 7 & 8 & 4.5 & 9 & 7 & 7 \\ \hline \end{array} $$ (a) Make a dotplot to display the data. (b) Describe the overall pattern of the distribution and any departures from that pattern.

The following table displays the total number of gold medals won by a sample of countries in the 2012 Summer Olympic Games in London. $$ \begin{array}{lclc} \hline & \text { Gold } & & \text { Gold } \\ \text { Country } & \text { medals } & \text { Country } & \text { medals } \\\ \text { Sri Lanka } & 0 & \text { Thailand } & 0 \\ \text { China } & 38 & \text { Kuwait } & 0 \\ \text { Vietnam } & 0 & \text { Bahamas } & 1 \\ \text { Great Britain } & 29 & \text { Kenya } & 2 \\ \text { Norway } & 2 & \text { Trinidad and Tobago } & 1 \\ \text { Romania } & 2 & \text { Greece } & 0 \\ \text { Switzerland } & 2 & \text { Mozambique } & 0 \\ \text { Armenia } & 0 & \text { (azakhstan } & 7 \\ \text { Netherlands } & 6 & \text { Denmark } & 2 \\ \text { India } & 0 & \text { Latvia } & 1 \\ \text { Georgia } & 1 & \text { Czech Republic } & 4 \\ \text { Kyrgyzstan } & 0 & \text { Hungary } & 8 \\ \text { costa Rica } & 0 & \text { Sweden } & 1 \\ \text { Brazil } & 3 & \text { Uruguay } & 0 \\ \text { Uzbekistan } & 1 & \text { United States } & 46 \\ \hline \end{array} $$ (a) Make a dotplot to display these data. Describe the overall pattern of the distribution and any departures from that pattern. (b) Overall, 205 countries participated in the 2012 Summer Olympics, of which 54 won at least one gold medal. Do you believe that the sample of countries listed in the table is representative of this larger population? Why or why not?

When comparing two distributions, it would be best to use relative frequency histograms rather than frequency histograms when (a) the distributions have different shapes. (b) the distributions have different spreads. (c) the distributions have different centers. (d) the distributions have different numbers of observations. (e) at least one of the distributions has outliers.

Which of the following is the best reason for choosing a stemplot rather than a histogram to display the distribution of a quantitative variable? (a) Stemplots allow you to split stems; histograms don't. (b) Stemplots allow you to see the values of individual observations. (c) Stemplots are better for displaying very large sets of data. (d) Stemplots never require rounding of values. (e) Stemplots make it easier to determine the shape of a distribution.

In a September 28,2008 , article titled "Letting Our Fingers Do the Talking," the New York Times reported that Americans now send more text messages than they make phone calls. According to a study by Nielsen Mobile, "Teenagers ages 13 to 17 are by far the most prolific texters, sending or receiving 1742 messages a month." Mr. Williams, a high school statistics teacher, was skeptical about the claims in the article. So he collected data from his first-period statistics class on the number of text messages and calls they had sent or received in the past 24 hours. Here are the texting data: $$ \begin{array}{rrrrrrrrrrrrr} \hline 0 & 7 & 1 & 29 & 25 & 8 & 5 & 1 & 25 & 98 & 9 & 0 & 26 \\ 8 & 118 & 72 & 0 & 92 & 52 & 14 & 3 & 3 & 44 & 5 & 42 & \\ \hline \end{array} $$ (a) Make a boxplot of these data by hand. Be sure to check for outliers. (b) Explain how these data seem to contradict the claim in the article.

Multiple choice: The scores on a statistics test had a mean of 81 and a standard deviation of \(9 .\) One student was absent on the test day, and his score wasn't included in the calculation. If his score of 84 was added to the distribution of scores, what would happen to the mean and standard deviation? (a) Mean will increase, and standard deviation will increase. (b) Mean will increase, and standard deviation will decrease. (c) Mean will increase, and standard deviation will stay the same. (d) Mean will decrease, and standard deviation will increase. (e) Mean will decrease, and standard deviation will decrease.