2.80Consider columns 1 and 3 of the energy-consumption data given in Exercise2.24.Compute the midpoint for each class presented in column 1.Pair eachmidpoint with its corresponding relative frequency found in column 3.Construct a horizontal axis, where the units are in terms of midpoints and avertical axis where the units are in terms of relative frequencies.Foreach midpoint on the horizontal axis, plot a point whose height is equal tothe relative frequency of the class.Then join the points with connectinglines.The result is a relative-frequency polygon.
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46
Chapter 2, Descriptive Statistics
2.81
(a)Consider all three columns of the energy-consumption data given inExercise 2.24.
(b)Pair each cutpoint in reworked column 1 with its correspondingcumulative relative frequency found in reworked column 3.Construct ahorizontal axis, where the units are in terms of the cutpoints and avertical axis where the units are in terms of cumulative relativefrequencies.For each cutpoint on the horizontal axis, plot a pointwhose height is equal to the cumulative relative frequency.Then jointhe points with connecting lines.The result, presented in Figure(b), is anogiveusing cumulative relative frequencies.(Note: Asimilar procedure could be followed using cumulative frequencies.)
Residential Energy Consumption
0.00
0.05
0.10
0.15
0.20
0.25
35
45
55
65
75
85
95 105 115 125 135 145 155 165
BTU (Millions)
Relative Frequency
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Section 2.3, Graphs and Charts
47
Residential Energy Consumption
0
0.2
0.4
0.6
0.8
1
1.2
20 30 40 50 60 70 80 90 10
0
11
0
12
0
13
0
14
0
15
0
16
0
BTU (Millions)
Cumulative Relative
Frequency
2.82
(a)
After rounding each weight to the nearest
integer (Any weight ending in
.5 is rounded up.), the stem-and-leaf diagram for the rounded weights
is
12
9
13
27
14
366
15
011599
16
12567
17
003445689
18
235789
19
1
20
9
21
58
22
23
24
25
26
27
9
(b)
After truncating each weight, the stem-and-leaf diagram for the rounded
weights is
12
9
13
26
14
2569
15
01588
16
11557
17
002335588
18
225778
19
1
20
9
21
48
22
23
24
25
26
27
8

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