Post on 26-Dec-2015
S2A
Chapter 7
More about Statistical Graphs
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Terminologies about Classes
19.5 24.5
Lower class
boundary
Upper class
boundary
20 2415 19 25 2920 24
Upper and lower class limits
Class width 24.5 19.5 5
Class mark
22
22420
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Frequency Distribution TableWaiting Time of 100 Passengers at a Bus Stop
Waiting time (min)
Class boundaries (min)
Class mark (min) Frequency
5 - 9 4.5 - 9.5 7 16
10 - 14 9.5 - 14.5 12 18
15 - 19 14.5 - 19.5 17 20
20 - 24 19.5 - 24.5 22 17
25 - 29 24.5 - 29.5 27 14
30 - 34 29.5 - 34.5 32 11
35 - 39 34.5 - 39.5 37 4
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Frequency Polygons
2009 Chung Tai Educational Press. All rights reserved.©
Cumulative Frequency Table
Waiting time less than (min) Cumulative frequency
4.5 0
9.5 16
14.5 34
19.5 54
24.5 71
29.5 85
34.5 96
39.5 100
2009 Chung Tai Educational Press. All rights reserved.©
Waiting Time of 100 Passengers at a Bus Stop
0
20
40
60
80
100
120
4.5 9.5 14.5 19.5 24.5 29.5 34.5 39.5
Waiting time (min)
Cum
ulat
ive
freq
uenc
yCumulative Frequency Polygon
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Percentiles
• Percentile represents a given percentage of the data less than a given value.
2009 Chung Tai Educational Press. All rights reserved.©
Change the cumulative frequency to percentage.
For example: 74% of students got the examination scores below 66.4.
Percentiles
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
2009 Chung Tai Educational Press. All rights reserved.©
• The score of 66.4 is called the 74th percentile and is denoted by P74. It means 74% of S2 students have scores less than 66.4.
• If there are 200 students in total, there are 148 (74% 200) students have scores less than 66.4.
Percentiles
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Quartiles• The percentiles P25, P50 and P75 divide the
number of data into 4 equal parts, so they are called quartiles.
• P25 is also called the lower quartile (denoted by
Q1).
• P50 is also called the median (denoted by Q2).
• P75 is also called the upper quartile (denoted by
Q3).
The End