Stat 101 – Sheet 4
King Saud University
Almajmaa’h Engineering College
STAT 101
1430/2009
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Sheet (5)
1. Briefly describe how the three quartiles are calculated for a data set.
Illustrate by calculating the three quartiles for two examples, the first with
an odd number of observations and the second with an even number of
observations.
2. Explain how the interquartile range is calculated. Give one example
3. The following data give the weights (in pounds) lost by 15 members of a
health club at the end of two months after joining the club.
5 10 8 7 25 5 14
11 10 21 8 11 18
a) Compute the values of the three quartiles and the interquartile range.
b) Calculate the (approximate) value of the 82nd percentile.
c) Find the percentile rank of 10
4. The following data give the speeds of 13 cars, measured by radar,
traveling on the highway in mile/hr
73 75 69 78 69 74
76 72 79 68 77 71
a) Find the values of the three quartiles and the interquartile range.
b) Calculate the (approximate) value of the 35th percentile.
c) Find the percentile rank of 71
Answer:
a) Q1 = 69; Q2 = 73; Q3 = 76.5; IQR = 7.5
b) P35 = 71
c) 30.77%
Dr. SaMeH
Page 1
Stat 101 – Sheet 4
5. The following data give the numbers of computer keyboards assembled at
the Twentieth Century Electronics Company for a sample of 25 days.
45 52 48 41 56 46 44 42 48 53
51 53 51 48 46 43 52 50 54 47
44 47 50 49 52
a) Find the values of the three quartiles and the interquartile range.
b) Calculate the (approximate) value of the 53th percentile.
c) Find the percentile rank of 50
6. The following data give the number of runners left on bases by each of
the 30 Major League Baseball teams in the games played on August 12,
2004.
6 6 6 7 6 10 6 3 6 8
10 7 18 11 6 9 4 8 9 5
5 4 8 8 8 5 5 5 13 8
a) Find the values of the three quartiles and the interquartile range.
b) Calculate the (approximate) value of the 63th percentile.
c) Find the percentile rank of 10
Answer:
a) Q1 = 5; Q2 = 6.5; Q3 = 8; IQR = 3
b) P35 = 8
c) 83.33%
7. The following data give the numbers of new cars sold at a dealership
during a 20-day period.
8 5 12 3 9 10 6 12 8 8
4 16 10 11 7 7 3 5 9 11
a) Find the values of the three quartiles and the interquartile range. Where
does the value of 4 lie in relation to these quartiles?
b) Calculate the (approximate) value of the 63th percentile. Give a brief
interpretation of this percentile.
c) Find the percentile rank of 10. Give a brief interpretation of this
percentile rank.
Dr. SaMeH
Page 2