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Unformatted text preview: Chapter 1 Solutions 1.1. (a) The individuals are vehicles (or “cars”). (b) The variables are make/model (categorical), vehicle type (categorical), transmission type (categorical), number of cylinders (quantitative), city mpg (quantitative), and highway mpg (quantitative). 1.2. Possible categorical variables: year in school, gender, major. Possible quantitative variables: age (years), time watching TV (hours), time in class (hours), time sleeping (hours), time studying (hours—or perhaps minutes). 1.3. (a) The given percentages add up to 90%, so 10% must be some other color. (b) The bar graph shown does not include the “other” category, although it certainly could be included. With the “other” category, a pie chart could be used because these percentages show parts of a whole (if we assume, as we did in part (a), that a car can be only one color). Silver White Black Blue Brown Red Yellow 5 10 15 20 Percent of 2005 cars 1.4. A pie graph could also be made, but the relative heights of the bars are easier to compare than the relative sizes of the “slices” of the pie. The most likely explanation for the lower weekend numbers is that, when a birth is “planned” (either by inducement or cesarean section), it is usually scheduled for a weekday—perhaps more due to the preferences of the physician or midwife. Sun Mon Tues Wed Thurs Fri Sat 2000 4000 6000 8000 10000 12000 Number of births 1.5. In order to know what percent of owners of portable MP3 players are 18 to 24 years old, we would need to know two things: the number of people who own MP3 players, and the number of those owners in that age group. The Arbitron data tells us neither of those things. 63 64 Chapter 1 Picturing Distributions with Graphs 1.6. With the intervals 15–16.9, 17–18.9, etc., the histogram should look like the one on the right. When asked to make intervals that are 2 minutes wide, some students might use 15–17, 17–19, etc., which causes confusion about where to place the three states (Illinois, Oregon, and South Carolina) that fall on an interval boundary. If a student’s histogram looks different from this one, that may be the reason. 13 15 17 19 21 23 25 27 29 31 33 2 4 6 8 10 12 14 Frequency Average travel time (minutes) 1.7. (a) The applet creates a histogram with 23 classes. (b) It is possible to get to one class ranging from 17 to 44.30 (not a very useful histogram). (c) The most classes the applet will allow is 46; the largest classes have 5 observations. (d) Choices will vary; anything from about 10 to 30 classes is reasonable....
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- Fall '09
- Bar chart, Categorical distribution