Statistics 20: Quiz 1 Solutions
Speed (mph)
Percentage of Total Cars
010
20
1020
10
2040
40
4080
20
8095
10
The above table depicts data collected in a (hypothetical) survey studying the distribution of traffic
speed on the Bay Bridge. Each group includes the left endpoint but not the right. (So, for instance,
the first group includes cars driving 0 mph (not moving) but does not include cars driving exactly
10 mph.) Use this information to answer Questions 13. You may draw a histogram of these data
if it helps you, but it is not necessary for answering the questions.
1. Would you estimate that there are more cars driving less than 1 mph than cars driving be
tween 21 and 22 mph? Note: the interval is [21,22).
For any class interval, we estimate the proportion of data falling in one of its subintervals by
the equation
Percent in subinterval = Percent in class
*
Length of SubInterval
Length of class interval
.
Based upon this, the percent of data in [0
,
1] is approximately 20%
1

0
10

0
= 2%.
Likewise, the percent of data in [21
,
22) is approximately 40%
22

21
40

20
= 2%.
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 Spring '08
 anderes
 Statistics, Approximation, Standard Deviation

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