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Mean from a Frequency Table. Calculating the Mean : If there are large amounts of data, it is easier if it is displayed in a frequency table. Example 1. The number of goals scored by a team in 20 games are given below : - PowerPoint PPT Presentation
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14
8
9
4
0
Example 1.The number of goals scored by a team in 20 games are given below :3 , 2 , 4 , 2 , 2 , 3 , 2 , 2 , 0 , 5 , 1 , 1 , 2 , 3 , 0 , 2 , 1 , 4 , 1 , 0
Mean from a Frequency Table
f.xFrequency, fGoals x
Calculating the Mean: If there are large amounts of data, it is easier if it is displayed in a frequency table.
0
1
2
3
4
5
3
4
7
3
2
1 5
∑f= 20 ∑fx= 40
Mean =∑fx
∑f
= 40
20= 2
Mode
14
19
17
7
3
Example 1.The number of goals scored by a team in 20 games are given below :3 , 2 , 4 , 2 , 2 , 3 , 2 , 2 , 0 , 5 , 1 , 1 , 2 , 3 , 0 , 2 , 1 , 4 , 1 , 0
Median from a Frequency Table
C. F.Frequency, fGoals x
Calculating the median If there are large amounts of data, it is easier if it is displayed in a frequency table.
0
1
2
3
4
5
3
4
7
3
2
1 20
∑f= 20Mode
(20)/2= 10
(20)/2 + 1= 11
The 10th value is 2The 11th value is 2∴ MEDIAN = ( 2+2 ) / 2 = 4/2 = 2
Large quantities of data can be much more easily viewed and managed if placed in groups in a frequency table. Grouped data does not enable exact values for the mean, median and mode to be calculated. Alternate methods of analyising the data have to be employed.
Example 1.During 3 hours at Heathrow airport 55 aircraft arrived late. The number of minutes they were late is shown in the grouped frequency table below.
Grouped Data
250 - 59
440 - 49
530 - 39
720 - 29
1010 - 19
270 - 9
frequencyminutes lateData is grouped into 6 class intervals of width 10.
Example 1.During 3 hours at Heathrow airport 55 aircraft arrived late. The number of minutes they were late is shown in the grouped frequency table below.
Grouped Data
midpoint(c.c.) F × c.c.
250 - 59
440 - 49
530 - 39
720 - 29
1010 - 19
270 - 9
Frequency,fminutes Late
Estimating the Mean: An estimate for the mean can be obtained by assuming that each of the raw data values takes the midpoint value of the interval in which it has been placed.
4.5
14.524.534.5
44.5
54.5
121.5
145
171.5172.5
178
109
Mean estimate = 897.5/55 ≈ 16.32 minutes
55f 5.897..ccf
Example 1.During 3 hours at Heathrow airport 55 aircraft arrived late. The number of minutes they were late is shown in the grouped frequency table below.
Grouped Data
The Modal Class
250 - 59
440 - 49
530 - 39
720 - 29
1010 - 19
270 - 9
frequencyminutes late
The modal class is simply the class interval of highest frequency.
Modal class = 0 - 9
For the following set of data find : أوجد التالية البيانات لمجموعة : بالنسبة
worksheet
الوسيط (2
المنوال (3
المدى (4
الحسابي (1 المتوسط6 , 8 , 5 , 11 , 3 , 1 , 7 , 9 , 3
1) The mean
2) The median
3) The mode
4) The range
أوجد التالية البيانات لمجموعة : For the following set of data find: بالنسبة
9 , 3 , 8 , 7 , 1 , 9 , 11 , 4 , 3 , 2
الوسيط (2
المنوال (3
المدى (4
الحسابي (1 The mean (1المتوسط
2) The median
3) The mode
4) The range
The ages of a random sample of 30 persons are given in the table :
Age ( x ) ( f ) X . f ( c f )
40 2
41 7
42 9
43 6
44 5
45 1
total
من عشوائية عينة كما 30أعمار شخص: بالجدول
: أوجد
worksheet
الوسيط (2 لألعمار
المنوال (3
مدى (4األعمار
الحسابي (1 المتوسطلألعمار
Find :
1) The mean age
2) The median
3) The mode
4) The range of the ages
The following frequency distribution represents the lengths of 20 persons
intervals ( f ) c.c. c.c.× f
150 - 154 2
155 - 159 8
160 - 164 5
165 - 169 4
170 - 179 1
total
أطوال يمثل التكراري شخص 20التوزيع
: أوجد
worksheet
وقدر (2 المنوالية الفئة اكتب المنوال
مدى (3 أوجداألطوال
الحسابي (1 المتوسطلألطوال
Find :
1) The mean of the lengths
2) The model class and estimate the mode
3) The range of the lengths
The grades of 25 students are given below :
Intervalsالفئات
( f ) ( c f )
total
يلي طالب 25درجات كما :
worksheet
التكراري (2 المضلع ارسمقيمة (3التراكمي لتقدر الرسم استخدمالوسيط
فئات (1 ذو تكراري جدول في الدرجات ضع1) Put the grades in a frequency table with intervals
2) Draw the cumulative frequency polygon
3) Use the graph to estimate the median
42 , 63 , 47 , 77 , 46 , 71 , 68 , 83 , 91 , 55 , 67 , 66 , 63 , 57 , 50 , 69 , 73 , 82, 77 , 58 , 66 , 79 , 88 , 97 , 86
(55+1)/2= 28
Example 1.During 3 hours at Heathrow airport 55 aircraft arrived late. The number of minutes they were late is shown in the grouped frequency table below.
Grouped Data
The Median Class Interval
The Median Class Interval is the class interval containing the median.
250 - 59
440 - 49
530 - 39
720 - 29
1010 - 19
270 - 9
frequencyminutes late
The 28th data value is in the 10 - 19 class
Data is grouped into 8 class intervals of width 4.
Example 2.A group of University students took part in a sponsored race. The number of laps completed is given in the table below. Use the information to: (a) Calculate an estimate for the mean number of laps.(b) Determine the modal class.(c) Determine the class interval containing the median.
Grouped Data
136 - 40
231 – 35
2526 – 30
1721 – 25
2016 – 20
1511 – 15
96 – 10
21 - 5
frequency (x)number of laps
c.c. X fmidpoint(c.c)
136 - 40
231 – 35
2526 – 30
1721 – 25
2016 – 20
1511 – 15
96 – 10
21 - 5
frequencynumber of laps
Example 2.A group of University students took part in a sponsored race. The number of laps completed is given in the table below. Use the information to: (a) Calculate an estimate for the mean number of laps.(b) Determine the modal class.(c) Determine the class interval containing the median.
Grouped Data
3
8
1318
23
2833
38
6
72195360
39170066
381828fx 91f
Mean estimate = 1828/91 = 20.1 laps
Modal Class 26 - 30
Grouped Data
Example 2.A group of University students took part in a sponsored race. The number of laps completed is given in the table below. Use the information to: (a) Calculate an estimate for the mean number of laps.(b) Determine the modal class. (c) Determine the class interval containing the median.
136 - 40
231 – 35
2526 – 30
1721 – 25
2016 – 20
1511 – 15
96 – 10
21 - 5
frequency (x)number of laps
136 - 40
231 – 35
2526 – 30
1721 – 25
2016 – 20
1511 – 15
96 – 10
21 - 5
frequency (x)number of laps
Example 2.A group of University students took part in a sponsored race. The number of laps completed is given in the table below. Use the information to: (a) Calculate an estimate for the mean number of laps.(b) Determine the modal class. (c) Determine the class interval containing the median.
Grouped Data
(91+1)/2 = 46
91f
The 46th data value is in the 16 – 20 class , median ≈ 18
c. F.
2
11
26
46
63
88
90
91