## Practice with Measures of Dispersion

Complete these exercises and check your answers.

### Questions

*Use the following information to answer the next nine exercises:* The population parameters below describe the full-time equivalent number of students (FTES) each year at Lake Tahoe Community College from 1976–1977 through 2004–2005.

*μ*= 1000 FTES- median = 1,014 FTES
*σ*= 474 FTES- first quartile = 528.5 FTES
- third quartile = 1,447.5 FTES
*n*= 29 years

94. The population standard deviation = _____

95. What percent of the FTES were from 528.5 to 1447.5? How do you know?

96. What is the

*IQR*? What does the*IQR*represent?97. How many standard deviations away from the mean is the median?

*Additional Information:* The population FTES for 2005–2006 through 2010–2011 was given in an updated report. The data are reported here.

Year |
2005–06 | 2006–07 | 2007–08 | 2008–09 | 2009–10 | 2010–11 |

Total FTES |
1,585 | 1,690 | 1,735 | 1,935 | 2,021 | 1,890 |

Table 2.73

Table 2.73

98. Calculate the mean, median, standard deviation, the first quartile, the third quartile, and the

*IQR*. Round to one decimal place.99. What additional information is needed to construct a box plot for the FTES for 2005-2006 through 2010-2011 and a box plot for the FTES for 1976-1977 through 2004-2005?

100. Compare the

*IQR*for the FTES for 1976–77 through 2004–2005 with the*IQR*for the FTES for 2005-2006 through 2010–2011. Why do you suppose the*IQR*s are so different?101. Three students were applying to the same graduate school. They came from schools with different grading systems. Which student had the best GPA when compared to other students at his school? Explain how you determined your answer.

Student | GPA | School Average GPA | School Standard Deviation |
---|---|---|---|

Thuy | 2.7 | 3.2 | 0.8 |

Vichet | 87 | 75 | 20 |

Kamala | 8.6 | 8 | 0.4 |

Table 2.74

Table 2.74

102. A music school has budgeted to purchase three musical instruments. They plan to purchase a piano costing $3,000, a guitar costing $550, and a drum set costing $600. The mean cost for a piano is $4,000 with a standard deviation of $2,500. The mean cost for a guitar is $500 with a standard deviation of $200. The mean cost for drums is $700 with a standard deviation of $100. Which cost is the lowest, when compared to other instruments of the same type? Which cost is the highest when compared to other instruments of the same type. Justify your answer.

103 . An elementary school class ran one mile with a mean of 11 minutes and a standard deviation of three minutes. Rachel, a student in the class, ran one mile in eight minutes. A junior high school class ran one mile with a mean of nine minutes and a standard deviation of two minutes. Kenji, a student in the class, ran 1 mile in 8.5 minutes. A high school class ran one mile with a mean of seven minutes and a standard deviation of four minutes. Nedda, a student in the class, ran one mile in eight minutes.

- Why is Kenji considered a better runner than Nedda, even though Nedda ran faster than he?
- Who is the fastest runner with respect to his or her class? Explain why.

Source: Rice University, https://openstax.org/books/introductory-statistics/pages/2-homework

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