91Ó°ÊÓ

In Exercises 9–12, find the mean for the data items in the given frequency distribution. $$ \begin{array}{|c|c|} \hline \begin{array}{c} \text { Score } \\ \boldsymbol{x} \end{array} & \begin{array}{c} \text { Frequency } \\ \boldsymbol{f} \end{array} \\ \hline 1 & 1 \\ \hline 2 & 3 \\ \hline 3 & 4 \\ \hline 4 & 4 \\ \hline 5 & 6 \\ \hline 6 & 5 \\ \hline 7 & 3 \\ \hline 8 & 2 \\ \hline \end{array} $$

A college professor had students keep a diary of their social interactions for a week. Excluding family and work situations, the number of social interactions of ten minutes or longer over the week is shown in the following grouped frequency distribution. Use this information to solve Exercises 9-16. $$ \begin{array}{|c|c|} \hline \begin{array}{c} \text { Number of } \\ \text { Social Interactions } \end{array} & \text { Frequency } \\ \hline 0-4 & 12 \\ \hline 5-9 & 16 \\ \hline 10-14 & 16 \\ \hline 15-19 & 16 \\ \hline 20-24 & 10 \\ \hline 25-29 & 11 \\ \hline 30-34 & 4 \\ \hline 35-39 & 3 \\ \hline 40-44 & 3 \\ \hline 45-49 & 3 \\ \hline \end{array} $$ What is the class width?

In Exercises 9–12, find the mean for the data items in the given frequency distribution. $$ \begin{array}{|c|c|} \hline \begin{array}{c} \text { Score } \\ \boldsymbol{x} \end{array} & \begin{array}{c} \text { Frequency } \\ \boldsymbol{f} \end{array} \\ \hline 1 & 3 \\ \hline 2 & 4 \\ \hline 3 & 6 \\ \hline 4 & 8 \\ \hline 5 & 9 \\ \hline 6 & 7 \\ \hline 7 & 5 \\ \hline 8 & 2 \\ \hline 9 & 1 \\ \hline 10 & 1 \\ \hline \end{array} $$

Systolic blood pressure readings are normally distributed with a mean of 121 and a standard deviation of 15. (A reading above 140 is considered to be high blood pressure.) In Exercises 17-26, begin by converting any given blood pressure reading or readings into \(z\)-scores. Then use Table \(12.16\) on page 822 to find the percentage of people with blood pressure readings below \(148 .\)

Intelligence quotients (IQs) on the Stanford-Binet intelligence test are normally distributed with a mean of 100 and a standard deviation of 16. In Exercises 23-32, use the 68-95-99.7 Rule to find the percentage of people with IQs between 68 and 132 .

In Exercises 25-32, find the mode for each group of data items. If there is no mode, so state. \(7,4,3,2,8,5,1,3\)

A set of data items is normally distributed with a mean of 60 and a standard deviation of 8 . In Exercises 33-48, convert each data item to a z-score. 76

A set of data items is normally distributed with a mean of 60 and a standard deviation of 8 . In Exercises 33-48, convert each data item to a z-score. 92

A set of data items is normally distributed with a mean of 60 and a standard deviation of 8 . In Exercises 33-48, convert each data item to a z-score. 78

Describe why the range might not be the best measure of dispersion.