Solutions for the Required Problems
for Homework #2 from Chapter 3, Section 3.1
Required homework: Problems 9, 11, and 59 from Chapter 3 from section 3.1 and
the endofchapter supplementary exercise, with additional questions asked in the
assignment.
9. a.
6330
422
15
i
x
x
n
Σ
=
=
=
minutes
b.
Median is in the 8
th
ordered position of the ranked data, so the median is
380 minutes.
c.
Q
1
=
210.0 (as median of lower half,
Q
1
is in the 4
th
ordered position of the
lower half)
Q
3
=
615.0 (as median of upper half,
Q
3
is in the 4
th
ordered position of the
upper half)
No mode
Midquartile = (Q1 + Q3)/2 = (210.0 + 615.0)/2 = 412.5
d.
Using the mean
x
= 422, cellphone subscribers are using 422/750 = 56%
of the capacity of their plans. Part (c) shows 75% (the percentile
interpretation of
Q
3
) of the subscribers are using 615 minutes or less. In
general, cellphone users are not coming close to using the 750 minute
capacity of their plans.
Additional questions:
a.
What population (or populations) is sampled?
All cell phone users.
(The variable of interest is monthly usage, measured as minutes used per
month.
The data is quantitative and continuous, and is measured on a ratio
scale.)
b.
What value is expected of the sampled data?
Of the sampled data, expect a monthly usage of 422.0 minutes.
ASW 5e Sec 3.1 Req HW #2
1
© 2010 Harvey Singer
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In other words, in general, expect any cell phone user to use 422.0 minutes
per month.
c.
What value is expected in general?
In general, expect a monthly usage of 422.0 minutes.
d.
What assumptions did you have to make to answer the last question?
Representative sample, sampling was random.
e.
What are high values?
Values greater than 380 minutes are above median and in the upper half.
As a result, monthly usage greater than 380 minutes would be considered
high values representing “heavy” use.
What are the low values?
Why, including your basis of comparison?
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 Spring '08
 SINGER
 Harvey Singer, Req HW

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