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S2A Chapter 7 More about Statistical Graphs

2009 Chung Tai Educational Press. All rights reserved. © Terminologies about Classes 19.5 24.5 Lower class boundary Upper class boundary 20 2415 1925 29 20 24 Upper and lower class limits Class width  24.5  19.5  5 Class mark 22

2009 Chung Tai Educational Press. All rights reserved. © Frequency Distribution Table Waiting Time of 100 Passengers at a Bus Stop Waiting time (min) Class boundaries (min) Class mark (min) Frequency 5 - 94.5 - 9.5716 10 - 149.5 - 14.51218 15 - 1914.5 - 19.51720 20 - 2419.5 - 24.52217 25 - 2924.5 - 29.52714 30 - 3429.5 - 34.53211 35 - 3934.5 - 39.5374

2009 Chung Tai Educational Press. All rights reserved. © Cumulative Frequency Table Waiting time less than (min) Cumulative frequency 4.50 9.516 14.534 19.554 24.571 29.585 34.596 39.5100

2009 Chung Tai Educational Press. All rights reserved. © 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 P 74. 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

2009 Chung Tai Educational Press. All rights reserved. © Quartiles The percentiles P 25, P 50 and P 75 divide the number of data into 4 equal parts, so they are called quartiles. P 25 is also called the lower quartile (denoted by Q 1 ). P 50 is also called the median (denoted by Q 2 ). P 75 is also called the upper quartile (denoted by Q 3 ).

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