(e) The graph should resemble the given histogram.  We see two clusters, one centered around 52 minutes and one around 79 minutes.

(f) The different subinterval widths change the histogram's appearance dramatically. With 5 subintervals the two clusters are not apparent, and with 20
subintervals the distribution looks very jagged. The most informative picture is probably the histogram with 10 subintervals.

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Activity 9-1: Properties of Correlation (cont.)

Note, to calculate the correlations with the TI, cars that had any missing values were first deleted from the data set.  This leaves 72 cars.
 

	strongly positive		mildly positive		virtually none		mildly negative		strongly negative
letter:	B	F	I	E	C	H	A	G	D
r	.994	.887	.510	.232	-.067	-.167	-.452	-.685	-.888

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Activity 10-2: Airfares (cont.)

(b)

		mean	std. dev
airfare (y)		166.9	59.5
distance (x)		713	403

r = .795
(c) airfare = 83.479 + .117 * distance
(f) airfare = 83.479 + .117 * distance
(g) 83.479+.117(300) = $118.58
(h) $258.98
(i),(j) (from Minitab)

(k) Answers will vary from student to student, but a good estimate would be $190.
(l) $188.78
(m) $415.99;  This is probably not a reliable estimate since a distance of 2,842 miles is well beyond our data set.
(n)

distance	900	901	902	903
predicted airfare	$188.78	$188.89	$189.01	$189.13

(o) Each mile adds about another $0.11, which is close to the slope of our least squares regression line, .117.
(p) $11.70

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Activity 10-3 (cont.)

(j) sum of squared residuals: $14,308.09;
(k) sum of squared deviations from overall mean: $38,882.92
(l) .632
(m) .632;  This is the same as the proportion of variability in the response variable that is explained by the regression model.

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Activity 10-4 (cont.)
(c) Yes
(d) The line on the private college scatterplot appears to do a better job of summarizing the relationship between tuition and founding year.  The points follow the linear relationship much more closely.
(e) public: $5,083;  private: $14,229;  Judging from the scatterplot, the private school prediction seems more reasonable because the points fall closer to the line in the area of 1900 on this scatterplot.

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