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CH%204%20Solutions[1] - Chapter 4 Solutions 4.1(a Time...

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Chapter 4 Solutions 4.1. (a) Time spent studying is explanatory; the grade is the response variable. (b) Explore the relationship; there is no reason to view one or the other as explanatory. (c) Time spent on extracurricular activities is explanatory, GPA is the response variable. (d) Explore the relationship. 4.2. Water temperature is explanatory, and weight change (growth) is the response variable. Both are quantitative. 4.3. For example: Weight, gender, other food eaten by the students, type of beer (light, imported, ... ). 4.4. Check that students understand that the explanatory variable (returning birds) goes on the horizontal axis. 3 6 9 12 15 18 21 35 40 45 50 55 60 65 70 75 80 Count of new birds Percent of returning birds 4.5. The scatterplot (see the previous exercise) shows a linear, negative, fairly weak relationship. (Note: form = linear, direction = negative, strength = weak.) Because this association is negative, we conclude that the sparrowhawk is a long-lived territorial species. 4.6. (a) At right; speed is explanatory. (b) The relationship is curved—low in the middle, higher at the extremes. Because low “mileage” is actually good (it means that we use less fuel to travel 100 km), this makes sense: moderate speeds yield the best perfor- mance. Note that 60 km / hr is about 37 mph. (c) Above-average (that is, bad) values of “fuel used” are found with both low and high values of “speed.” (d) The relationship is very strong—there is little scatter around the curve, so the curve is very useful for prediction. 0 5 10 15 20 0 20 40 60 80 100 120 140 Fuel used (liters/100 km) Speed (km/hr) 87
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88 Chapter 4 Scatterplots and Correlation 4.7. (a) In the scatterplot on the right, the open circles represent Run 8905, the higher flow rate. (b) Icicles seem to grow faster when the water runs more slowly. (Note that there is no guarantee that the pattern we observe with these two flow rates applies to rates much faster than 29.6 mg / s, or slower than 11.9 mg / s.) o o o o o o o o o o o o o o o o o o o o o o o o 0 5 10 15 20 25 0 50 100 150 200 Icicle length (cm) Time (minutes) Run 8903 o Run 8905 4.8. (a) Price is explanatory (and so is on the horizontal axis). The plot shows a positive linear association. (b) x = 50 cents / lb and s x . = 16 . 3248 cents / lb; y = 1 . 738% and s y . = 0 . 9278%. The standardized values are below; the correlation is r = 3 . 8206 / 4 = 0 . 955. (c) Obviously, the calculator value should be the same.
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CH%204%20Solutions[1] - Chapter 4 Solutions 4.1(a Time...

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