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
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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:
A.M. (Arithmetic mean) is
i.e. product of mean & no. of items gives sum of observation.
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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.
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Sol.
So, the correct mean is 39.7
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Method for Mean of Ungrouped Data
Grouped Frequency Distribution (Grouped)
(i) Direct method : for finding mean mean
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Ex. 2 Find the missing value of
5 | 8 | 10 | 12 | 20 | 25 | ||
---|---|---|---|---|---|---|---|
2 | 5 | 8 | 22 | 7 | 4 | 2 |
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Sol. Given
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Ex. 3 Find the mean for the following distribution :
Marks | |||||||
---|---|---|---|---|---|---|---|
Frequency | 6 | 8 | 13 | 7 | 3 | 2 | 1 |
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Sol.
Marks | Mid Values |
No. of students |
|
---|---|---|---|
25 | |||
35 | |||
45 | |||
55 | |||
65 | |||
75 | |||
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(ii) Deviation Method : (Assumed Mean Method)
where,
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Ex 4. Find the mean for the following distribution by using deviation method :
15 | 20 | 22 | 24 | 25 | 30 | 33 | 38 | |
---|---|---|---|---|---|---|---|---|
Frequency | 5 | 8 | 11 | 20 | 23 | 18 | 13 | 2 |
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Sol.
Let |
|||
---|---|---|---|
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 |
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(iii) Step - Deviation Method :
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Ex. 5 Find the mean of following distribution with step - deviation method :
Class | ||||||
---|---|---|---|---|---|---|
Frequency | 5 | 6 | 8 | 12 | 6 | 3 |
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Sol. Calculation of Mean :
Class | Let |
|||
---|---|---|---|---|
10-15 | 12.5 | 5 | -3 | -15 |
17.5 | 6 | -2 | -12 | |
22.5 | 8 | -1 | -8 | |
27.5 | 12 | 0 | 0 | |
32.5 | 6 | 1 | 6 | |
37.5 | 3 | 2 | 6 | |
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Ex. 6 The mean of the following frequency distribution is 62.8 and the sum of all frequencies is 50. Compute the missing frequency
Class | ||||||
---|---|---|---|---|---|---|
Frequency | 5 | 10 | 7 | 8 |
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Sol. Let
Class | ||||
---|---|---|---|---|
10 | 5 | -1 | -5 | |
30 | 0 | 0 | ||
50 | 10 | +1 | 10 | |
70 | +2 | |||
90 | 7 | +3 | 21 | |
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Given
Now,
So, the missing frequencies are
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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 |
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Sol. Charging less than type frequency distribution in general frequency distribution.
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According to step deviation formula for mean
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14.4 PROPERTIES OF MEAN :
(i) Sum of deviations from mean is zero. i.e.
(ii) If a constant real number ’
(iii) If a constant real number ‘a’ is subtracted from each of the observation then new mean will be
(iv) If constant real number ’
(v) If each of the observation is divided by a constant no ’
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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.
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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.
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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.
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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 ’
(A) if
(B) if
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Median of class - interval data (Grouped)
Median
What is median class :
The class in which
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Ex.8. Following are the lives in hours of 15 pieces of the components of air craft engine. Fin the median :
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Sol. Arranging the data in ascending order
- 696, 705, 710, 712, 715, 716, 719, 724, 725, 728, 729, 734, 745
So, Median
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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.
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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 |
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Ex. 10 Calculate the median for the following distribution class :
Class | ||||||
---|---|---|---|---|---|---|
Frequency | 5 | 10 | 20 | 7 | 8 | 5 |
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Sol. (i) First we find
Median
Class | c.f. | |
---|---|---|
5 | 5 | |
10 | 15 | |
20 | 35 | |
7 | 42 | |
8 | 50 | |
5 | 55 |
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Ex. 11 in the median of the following frequency distribution is 46, find the missing frequencies :
Variable | Total | |||||||
---|---|---|---|---|---|---|---|---|
Frequency | 12 | 13 | 65 | 25 | 18 | 229 |
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Sol.
Class Interval | Frequency | C.F |
---|---|---|
12 | 12 | |
30 | 42 | |
65 | ||
25 | ||
18 |
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Let the frequency of the class
It is given that median is 46 ., clearly, 46 lies in the class
Median
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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.
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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.
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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
Where
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Ex.12. Fin the mode of the following data :
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Sol. Frequency table for the given data as given below :
Value |
15 | 16 | 18 | 19 | 20 | 21 | 22 | 24 | 25 | 34 | 48 |
---|---|---|---|---|---|---|---|---|---|---|---|
Frequency |
1 | 4 | 1 | 5 | 3 | 1 | 1 | 1 | 1 | 1 | 1 |
19 has the maximum frequency of 5 . So, Mode
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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) | ||||||
---|---|---|---|---|---|---|
No. of Cases | 6 | 11 | 21 | 23 | 14 | 5 |
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Sol.
Here class intervals are not is inclusive form. So, Converting the above frequency table in inclusive form.
Age (in Years) | ||||||
---|---|---|---|---|---|---|
No. of Cases | 6 | 11 | 21 | 23 | 14 | 5 |
Class 34.5 - 44.5 has maximum frequency. So it is the modal class.
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Ex. 14 Find the mode of following distribution :
Daily Wages | ||||||
---|---|---|---|---|---|---|
No. of workers | 6 | 12 | 20 | 15 | 9 | 4 |
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Sol.
Daily Wages | No. of workers | Daily wages | No of workers |
---|---|---|---|
6 | 6 | ||
12 | 12 | ||
20 | 20 | ||
15 | 15 | ||
9 | 9 | ||
4 | 4 |
Modal class frequency is 42.5 - 48.5 .
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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.
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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.
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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.
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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
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In ungrouped frequency distribution :
Ex. 15 The marks obtained by 400 students in medical entrance exam are given in the following table.
Marks Obtained |
||||||||
---|---|---|---|---|---|---|---|---|
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.
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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 |
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Following are the O-give for the above cumulative frequency table by applying the given method and the assumed scale.
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(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 |
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Following are the O-give for the above cumulative frequency table.
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(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 .
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Ex. 16 Draw on O-give for the following frequency distribution by less than method and also find its median from the graph.
Marks | ||||||
---|---|---|---|---|---|---|
Number of students |
7 | 10 | 23 | 51 | 6 | 3 |
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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 |
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According to graph median
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DAILY PRACTIVE PROBLEMS 14
OBJECTIVE DPP - 14.1
1. The median of following series if
(A) 1210
(B) 520
(C) 190
(D) 35
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Que. | 1 |
---|---|
Ans. | C |
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2. If the arithmetic mean of 5,7,9,
(A) 11
(B) 15
(C) 18
(D) 16
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Que. | 2 |
---|---|
Ans. | B |
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3. The mode of the distribution 3, 5, 7, 4, 2, 1, 4, 3, 4 is
(A) 7
(B) 4
(C) 3
(D) 1
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Que. | 3 |
---|---|
Ans. | B |
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4. If the first five elements of the set
Class | ||||||
---|---|---|---|---|---|---|
Frequency | 10 | 7 | 8 |
(A)
(B)
(C)
(D)
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Que. | 4 |
---|---|
Ans. | A |
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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
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Que. | 5 |
---|---|
Ans. | C |
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SUBJECTIVE DPP - 14.2
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1. Find the value of
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Sol. 1.
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2. Find the mean of following distribution by step deviation method :
Class interval | ||||||
---|---|---|---|---|---|---|
No. of workers | 18 | 12 | 13 | 27 | 8 | 22 |
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Sol. 2.
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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.
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Sol. 3.
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4. Calculate the median from the following data :
Rent (in Rs.) | ||||||||
---|---|---|---|---|---|---|---|---|
No. of House | 8 | 10 | 15 | 25 | 40 | 20 | 15 | 7 |
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Sol. 4.
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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 | 25 | 10 | 5 | 200 |
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Sol. 5.
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6. If the median of the following frequency distribution is 28.5 find the missing frequencies :
Class interval : | Total | ||||||
---|---|---|---|---|---|---|---|
Frequency | 5 | 20 | 15 | 5 | 60 |
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Sol. 6.
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7. The marks is science of 80 students of class
Class interval : |
100 |
|||||||||
---|---|---|---|---|---|---|---|---|---|---|
Frequency | 3 | 5 | 16 | 12 | 13 | 20 | 5 | 4 | 1 | 1 |
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Sol. 7.
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8. Find the mode of following distribution :
Class interval |
||||||||
---|---|---|---|---|---|---|---|---|
Frequency | 5 | 8 | 7 | 12 | 28 | 20 | 10 | 10 |
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Sol. 8.
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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.
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Sol. 9.
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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.
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11. If the mean of the following data is 18.75 , find the value of
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Sol. 11.
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12. Find the mean of following frequency distribution [CBSE - 2006]
Classes | ||||||
---|---|---|---|---|---|---|
Frequency | 18 | 12 | 13 | 27 | 8 | 22 |
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Sol. 12.
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13. Find the median class of the following data : [CBSE - 2008]
Marks obtained | ||||||
---|---|---|---|---|---|---|
Frequency | 8 | 10 | 12 | 22 | 30 | 18 |
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Sol. 13.
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14. Find the mean, mode and median of the following data : [CBSE - 2008]
Classes | |||||||
---|---|---|---|---|---|---|---|
Frequency | 5 | 10 | 18 | 30 | 20 | 12 | 5 |
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Sol. 14.