knowledge-route Maths10 Ch7


title: “Lata knowledge-route-Class10-Math1-2 Merged.Pdf(1)” type: “reveal” weight: 1

STATISTICS

STATISTICS

14.1 INTRODUCTION :

The branch of science known as statistics has been used in India from ancient times. Statistics deals with

collection of numerical facts. i.e., data, their classification & tabulation and their interpretation.

14.2 MEASURES OF CENTRAL TENDANCY :

The commonly used measure of central tendency (or averages) are :

(i) Arithmetic Mean (AM) or Simply Mean (ii) Median (iii) Mode

STATISTICS

14.3 ARITHMETIC MEAN : Arithmetic mean of a set of observations is equal to their sum divided by the total number of observations.

Mean of raw data: x1,x2,x3,..,xn are the n values (or observations) the,

A.M. (Arithmetic mean) is

x¯=x1+x1+..+xnn=i=1nxinnx¯ - Sum of observations =i=1nxin

i.e. product of mean & no. of items gives sum of observation.

STATISTICS

Ex. 1 The mean of marks scored by 100 students was found to be 40. Later on its was discovered that a score of 56 was misread as 83 . Find the correct mean.

STATISTICS

Sol. n=100,x¯=40

x=1n(xi)40=1100(xi)

Incorrect value of xi=4000. Now, Correct value of xi=400083+83=3970

Correct mean = correct value of xin=3970100=39.7

So, the correct mean is 39.7

STATISTICS

Method for Mean of Ungrouped Data

xi fi F1x1
x1 f1 f1x1
x2 f2 f2x2
x3 f3 f3x3
fi= f1x1=

Grouped Frequency Distribution (Grouped)

(i) Direct method : for finding mean mean x¯=fixifu

STATISTICS

Ex. 2 Find the missing value of P for the following distribution whose mean is 12.58

x 5 8 10 12 P 20 25
y 2 5 8 22 7 4 2

STATISTICS

Sol. Given x=12.58 Calculation of Mean :

xi fi fixi
5 2 10
8 5 40
10 8 80
12 22 264
P 7 7P
20 4 80
25 2 50
fi=50 fixu=524+7P

x¯=fixifi

12.58=524+7P50629=524+7P;7P=105;P=15.

STATISTICS

Ex. 3 Find the mean for the following distribution :

Marks 1020 2030 3040 4050 5060 6070 7080
Frequency 6 8 13 7 3 2 1

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Sol.

Marks Mid Values xi No. of students
fi
fixi
1020 15 6 90
2030 25 8 200
3040 35 13 455
4050 45 7 345
5060 55 3 165
6070 65 2 130
7080 75 1 75
fi=40 fixi=1430

STATISTICS

x¯=fixifi=143040=1434=35.75

(ii) Deviation Method : (Assumed Mean Method)

x¯=A+fidifi

where, A= Assumed mean di= Deviation from mean (xiA)

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Ex 4. Find the mean for the following distribution by using deviation method :

xi 15 20 22 24 25 30 33 38
Frequency 5 8 11 20 23 18 13 2

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Sol.

xi fi Let A=25
di=xi25
fidi
15 5 -10 -50
20 8 -5 -40
22 11 -3 -33
24 20 -1 -20
25 23 0 0
30 18 5 90
33 13 8 104
38 2 13 26
fi=100 fidi=77

STATISTICS

x¯=A+fidifi=25+77100=25.77

(iii) Step - Deviation Method : x¯=A+(fiuifi)h where,

A= Assumed mean ui=xiAh,h= Width of class interval 

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Ex. 5 Find the mean of following distribution with step - deviation method :

Class 1015 1520 2025 2530 3035 3540
Frequency 5 6 8 12 6 3

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Sol. Calculation of Mean :

Class xi fi Let A=27.5
ui=xi27.55
fiui
10-15 12.5 5 -3 -15
1520 17.5 6 -2 -12
2025 22.5 8 -1 -8
2530 27.5 12 0 0
3035 32.5 6 1 6
3540 37.5 3 2 6
fi=40 fiui=23

x=A+(fiuifi)hx=27.5+×(2340)=24.625

STATISTICS

Ex. 6 The mean of the following frequency distribution is 62.8 and the sum of all frequencies is 50. Compute the missing frequency f1 and f2

Class 020 2040 4060 6080 80100 100120
Frequency 5 f1 10 f2 7 8

STATISTICS

Sol. Let =30,h=20

Class xi fi ui=xiAh fiui
020 10 5 -1 -5
2040 30 f1 0 0
4060 50 10 +1 10
6080 70 f2 +2 2f2
80100 90 7 +3 21
100120 110 8 +4 32
fi=30+f1+f2 fiui=58+2f2

STATISTICS

Given 30+f1+f2=50

f1+f2=20 …(i)

x¯=A+(fiuifi×h)

62.8=30=(58+2f250×20)

62.8=(58+2f2)×25

32.8×5=116+4f2

164=116+4f2

4f2=164116

4f2=48

f2=12

Now, f1=f2=20 f1+12=20 f1=8

So, the missing frequencies are f1=8 and f2=12.

STATISTICS

Ex. 7 Find the mean marks from the following data :

Marks No. of Students
Below 10 5
Below 20 9
Below 30 17
Below 40 29
Below 50 45
Below 60 60
Below 70 70
Below 80 78
Below 90 83
Below 100 85

STATISTICS

Sol. Charging less than type frequency distribution in general frequency distribution.

alt text

STATISTICS

According to step deviation formula for mean

x¯=A+(fiuifi×h)

x¯=45+(2985×10)

x¯=45+3.41

x¯=48.41 So, the mean marks is 48.41

STATISTICS

14.4 PROPERTIES OF MEAN :

(i) Sum of deviations from mean is zero. i.e. i=1n(xix¯)=0

(ii) If a constant real number ’ a ’ is added to each of the observation than new mean will be x¯+a.

(iii) If a constant real number ‘a’ is subtracted from each of the observation then new mean will be x¯a.

(iv) If constant real number ’ a ’ is multiplied with each of the observation then new mean will be ax¯.

(v) If each of the observation is divided by a constant no ’ a ‘, then new mean will be x¯a.

STATISTICS

14.5 MERITS OF ARITHETIC MEAN :

(i) It is rigidly defined, simple, easy to understand and easy to calculate.

(ii) It is based upon all the observations.

(iii) Its value being unique, we can use it to compare different sets of data.

(iv) It is least affected by sampling fluctuations.

(v) Mathematical analysis of mean is possible. So, It is relatively reliable.

STATISTICS

14.6 DEMERITS OF ARITHMETCI MEAN :

(i) It can not be determined by inspection nor it can be located graphically.

(ii) Arithmetic mean cannot be used for qualities characteristics such as intelligence, honesty, beauty etc.

(iii) It cannot be obtained if a single observation is missing.

(iv) It is affected very much by extreme values. In case of extreme items, A.M. gives a distorted picture of the distribution and no longer remains representative of the distribution.

(v) It may lead to wrong conclusions if the details of the data from which it is computed are not given.

(vi) It can not be calculated if the extreme class is open, e.g. below 10 or above 90.

(vii) It cannot be used in the study of rations, rates etc.

STATISTICS

14.7 USES OF ARITHMETIC MEAN :

(i) It is used for calculating average marks obtained by a student.

(ii) It is extensively used in practical statistics and to obtain estimates.

(iii) It is used by businessman to find out profit per unit article, output per machine, average monthly income and expenditure etc.

STATISTICS

14.8 MEDIAN :

Median is the middle value of the distribution. It is the value of variable such that the number of observations above it is equal to the number of observations below it.

Median of raw data

(i) Arrange the data in ascending order.

(ii) Count the no. of observation (Let there be ’ n ’ observation)

(A) if n be odd then median = value of (n+12)th  observation.

(B) if n is even then median is the arithmetic mean of (n2)th  observation and (n2+1)th  observation.

STATISTICS

Median of class - interval data (Grouped)

Median =+N2Cf×h

= lower limit of median class, N= total no of observation

C= cumulative frequency of the class preceding the median class

h= size of the median class

f= frequency of the median class.

What is median class :

The class in which (N2)th  item lie is median class.

STATISTICS

Ex.8. Following are the lives in hours of 15 pieces of the components of air craft engine. Fin the median : 715,724,725,710,729,745,649,699,696,712,734,728,716,705,719

STATISTICS

Sol. Arranging the data in ascending order

  1. 696, 705, 710, 712, 715, 716, 719, 724, 725, 728, 729, 734, 745

N=15

So, Median =(N+12)th  observation =(15+12)th  observation

=716

STATISTICS

Ex. 9 The daily wages (in rupees) of 100 workers in a factory are given below :

Daily wages (in Rs.) 125 130 135 140 145 150 160 180
No. of workers 6 20 24 28 15 4 2 1

Find the median wage of a worker for the above date.

STATISTICS

Sol.

Daily wages (in Rs.) No. of workers Cumulative frequency
125 6 6
130 20 26
135 24 50
140 28 78
145 15 93
150 4 97
160 2 99
180 1 100

STATISTICS

N=100 (even)

 Median =(Nth2) observation +(N2+1)th  observation 2 Median =50th  observation +51th  observation 2=135+1402=137.50

Median wage of a workers in the factory is Rs 137.50 .

STATISTICS

Ex. 10 Calculate the median for the following distribution class :

Class 010 1020 2030 3040 4050 5060
Frequency 5 10 20 7 8 5

STATISTICS

Sol. (i) First we find (N2)th  value i.e. (552)th =27.5th  which lies in 20-30.

2030 class in median class here =20

N2=27.5,C=15,f=20,h=10 Median =20+2751520×10

Median =26.25

Class f c.f.
010 5 5
1020 10 15
2030 20 35
3040 7 42
4050 8 50
5060 5 55

STATISTICS

Ex. 11 in the median of the following frequency distribution is 46, find the missing frequencies :

Variable 1020 2030 3040 4050 5060 6070 7080 Total
Frequency 12 13 ? 65 ? 25 18 229

STATISTICS

Sol.

Class Interval Frequency C.F
1020 12 12
2030 30 42
3040 f1 42+f1
4050 65 107+f1
5060 f2 107+f1+f2
6070 25 132+f1+f2
7080 18 150+f1+f2

STATISTICS

Let the frequency of the class 3040 be f1 and that of the class 5060 be f2. The total frequency is 229

12+30+f1+65+f2+25+18=229

f1+f2=79

It is given that median is 46 ., clearly, 46 lies in the class 4050. So, 4050 is the median class

=40,h=10,f=65 and C=42+f1,N=229

Median =+N2Cf×h

46=40+2292(42+f1)65×10

46=40+1452f113

6=1452f113 2f1=67 f1=33.5 or 34

 Since, f1+f2=79f1=45

Hence,f1=34 and f2=45.

STATISTICS

Merits of Median :

(i) It is rigidly defined, easily, understood and calculate.

(ii) It is not all affected by extreme values.

(iii) It can be located graphically, even if the class - intervals are unequal.

(iv) It can be determined even by inspection is some cases.

STATISTICS

Demerits of Median :

(i) In case of even numbers of observations median cannot be determined exactly.

(ii) It is not based on all the observations.

(iii) It is not subject to algebraic treatment.

(iv) It is much affected by fluctuations of sampling.

Uses of Median :

(i) Median is the only average to be used while dealing with qualitative data which cannot be measured quantitatively but can be arranged in ascending or descending order of magnitude.

STATISTICS

14.9 MODE:

Mode or modal value of the distribution is that value of variable for which the frequency is maximum.

Mode of ungrouped data : - (By inspection only)

Arrange the data in an array and then count the frequencies of each variate.

The variant having maximum frequency is the mode.

Mode of continuous frequency distribution

Mode =+f1+f02f1f0f2×h

Where = lower limit of the modal class

f1= frequency of the class i.e. the largest frequency.

f0= frequency of the class preceding the modal class.

f2= frequency of the class succeeding the modal class.

h= width of the modal class

STATISTICS

Ex.12. Fin the mode of the following data :

25,16,19,48,19,20,34,15,19,20,21,24,19,16,22,16,18,20,16,19.

STATISTICS

Sol. Frequency table for the given data as given below :

Value xi 15 16 18 19 20 21 22 24 25 34 48
Frequency fi 1 4 1 5 3 1 1 1 1 1 1

19 has the maximum frequency of 5 . So, Mode =19.

STATISTICS

Ex.13. The following table shows the age distribution of cases of a certain disease admitted during a year in a particular hospital.

Age (in Years) 514 1524 2534 3544 4554 5564
No. of Cases 6 11 21 23 14 5

STATISTICS

Sol.

Here class intervals are not is inclusive form. So, Converting the above frequency table in inclusive form.

Age (in Years) 4.514.5 14.524.5 24.534.5 34.544.5 44.554.5 54.564.5
No. of Cases 6 11 21 23 14 5

Class 34.5 - 44.5 has maximum frequency. So it is the modal class.

34.5,h=10,f0=21,f1=23 and f2=14.

 Mode =+f1f02f1f0f2×h Mode =34.5+2321462114×10

=34.5+211×10

=36.31 Ans.

STATISTICS

Ex. 14 Find the mode of following distribution :

Daily Wages 3136 3742 4348 4954 5560 6166
No. of workers 6 12 20 15 9 4

STATISTICS

Sol.

Daily Wages No. of workers Daily wages No of workers
3136 6 30.536.5 6
3743 12 36.542.5 12
4348 20 42.548.5 20
4954 15 48.554.5 15
5560 9 54.560.6 9
6166 4 60.566.5 4

Modal class frequency is 42.5 - 48.5 .

l=42.5f1=20f0=12,f2=15,h=6 Mode =42.5+20122(20)1215×6

Mode =46.2

STATISTICS

Merits of Mode

(i) It can be easily understood and is easy to calculate.

(ii) It is not affected by extreme values and can be found by inspection is some cases.

(iii) It can be measured even if open - end classes and can be represented graphically.

STATISTICS

Demerits of Mode:

(i) It is ill - fined. It is not always possible to find a clearly defined mode.

(ii) It is not based upon all the observation.

(iii) It is not capable of further mathematical treatment. it is after indeterminate.

(iv) It is affected to a greater extent by fluctuations of sampling.

STATISTICS

Uses of Mode :

Mode is the average to be used to find the ideal size, e.g., in business forecasting, in manufacture of ready-made garments, shoes etc.

Relation between Mode, Median & Mean : Mode = 3 median - 2 mean.

STATISTICS

14.10 CUMULATIVE FREQUENCY CURVE OR OGIVE :

In a cumulative frequency polygon or curves, the cumulative frequencies are plotted against the lower and upper limits of class intervals depending upon the manner in which the series has been cumulated. There are two methods of constructing a frequency polygon or an Ogive.

(i) Less than method (ii) More than method

STATISTICS

In ungrouped frequency distribution :

Ex. 15 The marks obtained by 400 students in medical entrance exam are given in the following table.

Marks
Obtained
400450 450500 500550 550600 600650 650700 700750 75080
No. of
Examinees
30 45 60 52 54 67 45 47

(i) Draw Ogive by less than method.

(ii) Draw Ogive by more than method.

(iii) Find the number of examinees, who have obtained the marks less than 625.

(iv) Find the number of examinees, who have obtained 625 and more than marks.

STATISTICS

Sol. (i) Cumulative frequency table for less than Ogive method is as following.

Marks Obtained No. of Examinees
Less than 450 30
Less than 500 75
Less than 550 135
Less than 600 187
Less than 650 241
Less than 700 308
Less than 750 353
Less than 800 400

STATISTICS

Following are the O-give for the above cumulative frequency table by applying the given method and the assumed scale.

STATISTICS

(ii) Cumulative frequency table for more than Ogive method is as following : -

Marks Obtained No. of Examinees
400 and more 400
450 and more 370
500 and more 325
550 and more 265
600 and more 213
650 and more 159
700 and more 92
750 and more 47

STATISTICS

Following are the O-give for the above cumulative frequency table.

STATISTICS

(iii) So, the number of examinees, scoring marks less than 625 are approximately 220.

(iv) So, the number of examinees, scoring marks 625 and more will be approximately 190 .

STATISTICS

Ex. 16 Draw on O-give for the following frequency distribution by less than method and also find its median from the graph.

Marks 010 1020 2030 3040 4050 5060
Number of
students
7 10 23 51 6 3

STATISTICS

Sol. Converting the frequency distribution into less than cumulative frequency distribution.

Marks No. of
Students
Less than 10 7
Less than 20 17
Less than 30 40
Less than 40 91
Less than 50 97
Less than 60 100

STATISTICS

According to graph median =34 marks.

alt text

STATISTICS

DAILY PRACTIVE PROBLEMS 14

OBJECTIVE DPP - 14.1

1. The median of following series if 520,20,340,190,35,800,1210,50,80

(A) 1210

(B) 520

(C) 190

(D) 35

STATISTICS

Que. 1
Ans. C

STATISTICS

2. If the arithmetic mean of 5,7,9, x is 9 then the value of x is

(A) 11

(B) 15

(C) 18

(D) 16

STATISTICS

Que. 2
Ans. B

STATISTICS

3. The mode of the distribution 3, 5, 7, 4, 2, 1, 4, 3, 4 is

(A) 7

(B) 4

(C) 3

(D) 1

STATISTICS

Que. 3
Ans. B

STATISTICS

4. If the first five elements of the set x1,x2,x10 are replaced by xi+5,i=1,2,3,4,5 and next five elements are replaced by

Class 020 2040 4060 6080 80100 100120
Frequency 5 f1 10 f2 7 8

(A) 0

(B) n+12

(C) 10

(D) 25

STATISTICS

Que. 4
Ans. A

STATISTICS

5. If the mean and median of a set of numbers are 8.9 and 9 respectively, then the mode will be

(A) 7.2

(B) 8.2

(C) 9.2

(D) 10.2

STATISTICS

Que. 5
Ans. C

STATISTICS

SUBJECTIVE DPP - 14.2

STATISTICS

1. Find the value of p, if the mean of the following distribution whose mean is 20

x 15 17 19 20+p 23
f 2 3 4 5p 6

STATISTICS

Sol. 1. p=1

STATISTICS

2. Find the mean of following distribution by step deviation method :

Class interval 5070 7090 90110 110130 130150 150170
No. of workers 18 12 13 27 8 22

STATISTICS

Sol. 2. 112.20

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3. The mean of the following frequency distribution is 62.8 and the sum of all the frequencies is 50 . Compute the missing frequency.

STATISTICS

Sol. 3. f1=8,f2=12

STATISTICS

4. Calculate the median from the following data :

Rent (in Rs.) 1525 2535 3545 4555 5565 6575 7585 8595
No. of House 8 10 15 25 40 20 15 7

STATISTICS

Sol. 4. 58

STATISTICS

5. Find the missing frequencies and the median for the following distribution if the mean is 1.46.

No. of accidents 0 1 2 3 4 5 Total
Frequency (No. of
days)
46 f1 f2 25 10 5 200

STATISTICS

Sol. 5. f1=76,f2=38, and median =1

STATISTICS

6. If the median of the following frequency distribution is 28.5 find the missing frequencies :

Class interval : 010 1020 2030 3040 4050 5060 Total
Frequency 5 f1 20 15 f2 5 60

STATISTICS

Sol. 6. f1=8,f2=7

STATISTICS

7. The marks is science of 80 students of class X are given below : Find the mode of the marks obtained by the students in science.

Class
interval :
010 1020 2030 3040 4050 5060 6070 7080 8090 90
100
Frequency 3 5 16 12 13 20 5 4 1 1

STATISTICS

Sol. 7. 53.17

STATISTICS

8. Find the mode of following distribution :

Class
interval
010 1020 2030 3040 4050 5060 6070 7080
Frequency 5 8 7 12 28 20 10 10

STATISTICS

Sol. 8. 46.67

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9. During the medical check - up of 35 students of a class, their weights were recorded as follows :

Weight (in kg) Number of students
Less than 38 0
Less than 40 3
Less than 42 5
Less than 44 9
Less than 46 14
Less than 48 28
Less than 50 32
Less than 52 35

Draw a less than type ogive for the given data. Hence, obtain median weight from the graph and verify the result by using the formula.

STATISTICS

Sol. 9. 47.5kg

STATISTICS

10. The following table gives the height of trees :

Height Less
than 7
Les than
14
Less
than 21
Less
than 28
Less
than 35
Less
than 42
Less
than 49
Less
than 56
No. of trees 26 57 92 134 216 287 341 360

Draw “less than” ogive and “more than” ogive.

STATISTICS

11. If the mean of the following data is 18.75 , find the value of p : [CBSE - 2005]

x 10 15 P 25 30
f 5 10 7 8 2

STATISTICS

Sol. 11. 20

STATISTICS

12. Find the mean of following frequency distribution [CBSE - 2006]

Classes 5070 7090 90110 110130 130150 150170
Frequency 18 12 13 27 8 22

STATISTICS

Sol. 12. 20

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13. Find the median class of the following data : [CBSE - 2008]

Marks obtained 010 1020 2030 3040 4050 5060
Frequency 8 10 12 22 30 18

STATISTICS

Sol. 13. 3040

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14. Find the mean, mode and median of the following data : [CBSE - 2008]

Classes 010 1020 2030 3040 4050 5060 6070
Frequency 5 10 18 30 20 12 5

STATISTICS

Sol. 14. Mean =35.6, Median =35.67 and mode =35.45



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