Probability And Statistics Worksheets Page 28
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42E x a m p l e 2
Car Resale Values
100
SALES
Use the scatter plot at the right for these
80
questions.
60
a. What can you say about the correlation between the
age of a car and its resale value?
40
b. Predict the resale value of an 8-year-old car with an
20
original cost of $15,000.
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Solution
Age of Car
a. The trend line slopes downward from upper left to
lower right, so there is a negative correlation between a car’s age and its resale
value.
b. Extend the pattern. A reasonable assumption would be for the resale value to
be about 30% of the original cost for an 8-year-old car. So, a car that cost
$15,000 originally might sell for about $4500 after 8 years.
Another way to display data is with a box-and-whisker plot, also known as box plot.
This plot shows how data are dispersed around a median, but does not show
each specific item in the data. By examining a box-and-whisker plot, you can tell
if data are clustered closely together or spread far apart.
A box-and-whisker plot shows both the median and the extremes of a set of data.
It also shows the median of the lower half of the data, called the lower quartile,
and the median of the upper half of the data, called the upper quartile. Both
quartiles include the median if the data contain an odd number of items.
E x a m p l e 3
SPORTS
Joe DiMaggio played center field for the New York Yankees for 13 years.
During each year of his career, he hit the following number of home runs: 29, 46,
32, 30, 31, 30, 21, 25, 20, 39, 14, 32, and 12. Make a box-and-whisker plot for this
data.
Solution
Write the data in numerical order. Find the least and greatest values, the median,
the lower quartile, and the upper quartile.
least value
median
greatest value
12 14
20 21
25 29 30
30
31 32
32
39
46
lower quartile
upper quartile
Use points to mark the values below a number line. Draw a box
that starts and stops at the lower and upper quartiles, and a vertical
Check
line at the point for the median. Then draw whiskers, or line
Understanding
segments, from each end of the box to the least and greatest values.
Finally, give your graph a title.
In a box-and-whisker plot,
what percent of a set of
data is represented by the
DiMaggio’s Home Runs
box? By the whisker to
the right of the box?
12
21
30 32
46
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407
Lesson 9-6 Scatter Plots and Box-and-Whisker Plots
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