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Errors on a Typing Test. The distribution of the number of errors that 10 students made on a typing test is shown
Errors Frequency
0–2 1
3–5 3
6–8 4
9–11 1
12–14 1
Find each of these.
a. Mean = 6.4
b. Modal class = 6-8
c. Variance = 11.6
d. Standard deviation = 3.406
Inches of Rain Shown here is a frequency distribution for the number of inches of rain received in 1 year in 25 selected cities in the United States.
Number of inches Frequency
5.5–20.5 2
20.5–35.5 3
35.5–50.5 8
50.5–65.5 6
65.5–80.5 3
80.5–95.5 3
Find each of these.
a. Mean = 51.4
b. Modal class = 35.5 – 50.5
c. Variance = 451.5
d. Standard deviation = 21.249
. Shipment Times A survey of 36 selected recording companies showed these numbers of days that it took to receive a shipment from the day it was ordered.
Days Frequency
1–3 6
4–6 8
7–9 10
10–12 7
13–15 0
16–18 5
Find each of these.
a. Mean = 8.167
b. Modal class = 7-9
c. Variance = 21.57
d. Standard deviation = 4.645
27. Best Friends of Students In a survey of third-grade students, this distribution was obtained for the number of “best friends” each had.
Number of students Number of best friends
8 1
6 2
5 3
3 0
Find the average number of best friends for the class.
Use the weighted mean.
1.59
28. Employee Years of Service In an advertisement, a retail store stated that its employees averaged 9 years of service. The distribution is shown here.
Number of employees Years of service
8 2
2 6
3 10
Using the weighted mean, calculate the correct average.
4.46
29. Newspapers for Sale The average number of newspapers for sale in an airport newsstand is 12, and the standard deviation is 4. The average age of the pilots is 37 years, with a standard deviation of 6 years. Which data set is more variable?
The number of newspapers for sale
30. Brands of Toothpaste Carried A survey of grocery stores showed that the average number of brands of toothpaste carried was 16, with a standard deviation of 5. The same survey showed the average length of time each store was in business was 7 years, with a standard deviation of 1.6 years. Which is more variable, the number of brands or the number of years?
The number of brands of toothpaste
34. Exam Scores On a philosophy comprehensive exam, this distribution was obtained from 25 students.
Score Frequency
40.5–45.5 3
45.5–50.5 8
50.5–55.5 10
55.5–60.5 3
60.5–65.5 1
a. Construct a percentile graph.
Find the values that correspond to the 22nd, 78th, and 99th percentiles.
c. Find the percentiles of the values 52, 43,and 64.
|(a)Graph |
|[pic] |
|(b) 22nd percentile = 47.5 |
|78th percentile = 54 |
|99th percentile = 63.5 |
|[pic] |
|(c) 52 is 60th percentile, 43 is 0 percentile and 64 is 100th percentile |
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