Data Handling – II (Central Values Exercise 23.1) RD Sharma Solutions | Mathematics (Maths) Class 7 PDF Download

 Page 1


 
 
 
 
 
    
 
         
 
1. Ashish studies for 4 hours, 5 hours and 3 hours on three consecutive days. How 
many hours does he study daily on an average?  
 
Solution: 
Given Ashish studies for 4 hours, 5 hours and 3 hours on three consecutive days 
Average number of study hours = sum of hours/ number of days 
Average number of study hours = (4 + 5 + 3) ÷ 3 
= 12 ÷ 3 
= 4 hours 
Thus, Ashish studies for 4 hours on an average. 
 
2. A cricketer scores the following runs in 8 innings: 58, 76, 40, 35, 48, 45, 0, 100. 
Find the mean score. 
 
Solution: 
Given runs in 8 innings: 58, 76, 40, 35, 48, 45, 0, 100 
Mean score = total sum of runs/number of innings 
The mean score = (58 + 76 + 40 + 35 + 48 + 45 + 0 + 100) ÷ 8 
= 402 ÷ 8 
= 50.25 runs. 
 
3. The marks (out of 100) obtained by a group of students in science test are 85, 76, 
90, 84, 39, 48, 56, 95, 81 and 75. Find the 
(i) Highest and the lowest marks obtained by the students. 
(ii) Range of marks obtained. 
(iii) Mean marks obtained by the group. 
 
Solution: 
In order to find the highest and lowest marks, we have to arrange the marks in 
ascending order as follows: 
39, 48, 56, 75, 76, 81, 84, 85, 90, 95 
 
(i) Clearly, the highest mark is 95 and the lowest is 39. 
 
Page 2


 
 
 
 
 
    
 
         
 
1. Ashish studies for 4 hours, 5 hours and 3 hours on three consecutive days. How 
many hours does he study daily on an average?  
 
Solution: 
Given Ashish studies for 4 hours, 5 hours and 3 hours on three consecutive days 
Average number of study hours = sum of hours/ number of days 
Average number of study hours = (4 + 5 + 3) ÷ 3 
= 12 ÷ 3 
= 4 hours 
Thus, Ashish studies for 4 hours on an average. 
 
2. A cricketer scores the following runs in 8 innings: 58, 76, 40, 35, 48, 45, 0, 100. 
Find the mean score. 
 
Solution: 
Given runs in 8 innings: 58, 76, 40, 35, 48, 45, 0, 100 
Mean score = total sum of runs/number of innings 
The mean score = (58 + 76 + 40 + 35 + 48 + 45 + 0 + 100) ÷ 8 
= 402 ÷ 8 
= 50.25 runs. 
 
3. The marks (out of 100) obtained by a group of students in science test are 85, 76, 
90, 84, 39, 48, 56, 95, 81 and 75. Find the 
(i) Highest and the lowest marks obtained by the students. 
(ii) Range of marks obtained. 
(iii) Mean marks obtained by the group. 
 
Solution: 
In order to find the highest and lowest marks, we have to arrange the marks in 
ascending order as follows: 
39, 48, 56, 75, 76, 81, 84, 85, 90, 95 
 
(i) Clearly, the highest mark is 95 and the lowest is 39. 
 
 
 
 
 
 
    
 
(ii) The range of the marks obtained is: (95 – 39) = 56. 
 
(iii) From the following data, we have 
Mean marks = Sum of the marks/ Total number of students 
Mean marks = (39 + 48 + 56 + 75 + 76 + 81 + 84 + 85 + 90 + 95) ÷ 10 
= 729 ÷ 10 
= 72.9. 
Hence, the mean mark of the students is 72.9. 
 
4. The enrolment of a school during six consecutive years was as follows: 
1555, 1670, 1750, 2019, 2540, 2820 
Find the mean enrolment of the school for this period. 
 
Solution: 
Given enrolment of a school during six consecutive years as follows  
1555, 1670, 1750, 2019, 2540, 2820 
The mean enrolment = Sum of the enrolments in each year/ Total number of years 
The mean enrolment = (1555 + 1670 + 1750 + 2019 + 2540 + 2820) ÷ 6 
= 12354 ÷ 6 
= 2059. 
Thus, the mean enrolment of the school for the given period is 2059. 
 
5. The rainfall (in mm) in a city on 7 days of a certain week was recorded as follows: 
Day Mon Tue Wed Thu Fri Sat Sun 
Rainfall (in mm) 0.0 12.2 2.1 0.0 20.5 5.3 1.0 
(i) Find the range of the rainfall from the above data. 
(ii) Find the mean rainfall for the week. 
(iii) On how many days was the rainfall less than the mean rainfall. 
 
Solution: 
(i) The range of the rainfall = Maximum rainfall – Minimum rainfall 
= 20.5 – 0.0 
= 20.5 mm. 
 
(ii) The mean rainfall = (0.0 + 12.2 + 2.1 + 0.0 + 20.5 + 5.3 + 1.0) ÷ 7 
= 41.1 ÷ 7 
= 5.87 mm. 
Page 3


 
 
 
 
 
    
 
         
 
1. Ashish studies for 4 hours, 5 hours and 3 hours on three consecutive days. How 
many hours does he study daily on an average?  
 
Solution: 
Given Ashish studies for 4 hours, 5 hours and 3 hours on three consecutive days 
Average number of study hours = sum of hours/ number of days 
Average number of study hours = (4 + 5 + 3) ÷ 3 
= 12 ÷ 3 
= 4 hours 
Thus, Ashish studies for 4 hours on an average. 
 
2. A cricketer scores the following runs in 8 innings: 58, 76, 40, 35, 48, 45, 0, 100. 
Find the mean score. 
 
Solution: 
Given runs in 8 innings: 58, 76, 40, 35, 48, 45, 0, 100 
Mean score = total sum of runs/number of innings 
The mean score = (58 + 76 + 40 + 35 + 48 + 45 + 0 + 100) ÷ 8 
= 402 ÷ 8 
= 50.25 runs. 
 
3. The marks (out of 100) obtained by a group of students in science test are 85, 76, 
90, 84, 39, 48, 56, 95, 81 and 75. Find the 
(i) Highest and the lowest marks obtained by the students. 
(ii) Range of marks obtained. 
(iii) Mean marks obtained by the group. 
 
Solution: 
In order to find the highest and lowest marks, we have to arrange the marks in 
ascending order as follows: 
39, 48, 56, 75, 76, 81, 84, 85, 90, 95 
 
(i) Clearly, the highest mark is 95 and the lowest is 39. 
 
 
 
 
 
 
    
 
(ii) The range of the marks obtained is: (95 – 39) = 56. 
 
(iii) From the following data, we have 
Mean marks = Sum of the marks/ Total number of students 
Mean marks = (39 + 48 + 56 + 75 + 76 + 81 + 84 + 85 + 90 + 95) ÷ 10 
= 729 ÷ 10 
= 72.9. 
Hence, the mean mark of the students is 72.9. 
 
4. The enrolment of a school during six consecutive years was as follows: 
1555, 1670, 1750, 2019, 2540, 2820 
Find the mean enrolment of the school for this period. 
 
Solution: 
Given enrolment of a school during six consecutive years as follows  
1555, 1670, 1750, 2019, 2540, 2820 
The mean enrolment = Sum of the enrolments in each year/ Total number of years 
The mean enrolment = (1555 + 1670 + 1750 + 2019 + 2540 + 2820) ÷ 6 
= 12354 ÷ 6 
= 2059. 
Thus, the mean enrolment of the school for the given period is 2059. 
 
5. The rainfall (in mm) in a city on 7 days of a certain week was recorded as follows: 
Day Mon Tue Wed Thu Fri Sat Sun 
Rainfall (in mm) 0.0 12.2 2.1 0.0 20.5 5.3 1.0 
(i) Find the range of the rainfall from the above data. 
(ii) Find the mean rainfall for the week. 
(iii) On how many days was the rainfall less than the mean rainfall. 
 
Solution: 
(i) The range of the rainfall = Maximum rainfall – Minimum rainfall 
= 20.5 – 0.0 
= 20.5 mm. 
 
(ii) The mean rainfall = (0.0 + 12.2 + 2.1 + 0.0 + 20.5 + 5.3 + 1.0) ÷ 7 
= 41.1 ÷ 7 
= 5.87 mm. 
 
 
 
 
 
    
 
 
(iii) Clearly, there are 5 days (Mon, Wed, Thu, Sat and Sun), when the rainfall was less 
than the mean, i.e., 5.87 mm. 
 
6. If the heights of 5 persons are 140 cm, 150 cm, 152 cm, 158 cm and 161 cm 
respectively, find the mean height. 
 
Solution: 
The mean height = Sum of the heights /Total number of persons 
= (140 + 150 + 152 + 158 + 161) ÷ 5 
= 761 ÷ 5 
= 152.2 cm. 
 
7. Find the mean of 994, 996, 998, 1002 and 1000. 
 
Solution: 
Mean = Sum of the given numbers/Total number of given numbers 
Mean = (994 + 996 + 998 + 1002 + 1000) ÷ 5 
= 4990 ÷ 5 
= 998. 
 
8. Find the mean of first five natural numbers. 
 
Solution: 
We know that first five natural numbers = 1, 2, 3, 4 and 5 
Mean of first five natural numbers = (1 + 2 + 3 + 4 + 5) ÷ 5 
= 15 ÷ 5 
= 3 
 
9.  Find the mean of all factors of 10. 
 
Solution: 
We know that factors of 10 are 1, 2, 5 and 10 
Arithmetic mean of all factors of 10 = (1 + 2 + 5 + 10) ÷ 4 
= 18 ÷ 4 
= 4.5 
 
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1. Ashish studies for 4 hours, 5 hours and 3 hours on three consecutive days. How 
many hours does he study daily on an average?  
 
Solution: 
Given Ashish studies for 4 hours, 5 hours and 3 hours on three consecutive days 
Average number of study hours = sum of hours/ number of days 
Average number of study hours = (4 + 5 + 3) ÷ 3 
= 12 ÷ 3 
= 4 hours 
Thus, Ashish studies for 4 hours on an average. 
 
2. A cricketer scores the following runs in 8 innings: 58, 76, 40, 35, 48, 45, 0, 100. 
Find the mean score. 
 
Solution: 
Given runs in 8 innings: 58, 76, 40, 35, 48, 45, 0, 100 
Mean score = total sum of runs/number of innings 
The mean score = (58 + 76 + 40 + 35 + 48 + 45 + 0 + 100) ÷ 8 
= 402 ÷ 8 
= 50.25 runs. 
 
3. The marks (out of 100) obtained by a group of students in science test are 85, 76, 
90, 84, 39, 48, 56, 95, 81 and 75. Find the 
(i) Highest and the lowest marks obtained by the students. 
(ii) Range of marks obtained. 
(iii) Mean marks obtained by the group. 
 
Solution: 
In order to find the highest and lowest marks, we have to arrange the marks in 
ascending order as follows: 
39, 48, 56, 75, 76, 81, 84, 85, 90, 95 
 
(i) Clearly, the highest mark is 95 and the lowest is 39. 
 
 
 
 
 
 
    
 
(ii) The range of the marks obtained is: (95 – 39) = 56. 
 
(iii) From the following data, we have 
Mean marks = Sum of the marks/ Total number of students 
Mean marks = (39 + 48 + 56 + 75 + 76 + 81 + 84 + 85 + 90 + 95) ÷ 10 
= 729 ÷ 10 
= 72.9. 
Hence, the mean mark of the students is 72.9. 
 
4. The enrolment of a school during six consecutive years was as follows: 
1555, 1670, 1750, 2019, 2540, 2820 
Find the mean enrolment of the school for this period. 
 
Solution: 
Given enrolment of a school during six consecutive years as follows  
1555, 1670, 1750, 2019, 2540, 2820 
The mean enrolment = Sum of the enrolments in each year/ Total number of years 
The mean enrolment = (1555 + 1670 + 1750 + 2019 + 2540 + 2820) ÷ 6 
= 12354 ÷ 6 
= 2059. 
Thus, the mean enrolment of the school for the given period is 2059. 
 
5. The rainfall (in mm) in a city on 7 days of a certain week was recorded as follows: 
Day Mon Tue Wed Thu Fri Sat Sun 
Rainfall (in mm) 0.0 12.2 2.1 0.0 20.5 5.3 1.0 
(i) Find the range of the rainfall from the above data. 
(ii) Find the mean rainfall for the week. 
(iii) On how many days was the rainfall less than the mean rainfall. 
 
Solution: 
(i) The range of the rainfall = Maximum rainfall – Minimum rainfall 
= 20.5 – 0.0 
= 20.5 mm. 
 
(ii) The mean rainfall = (0.0 + 12.2 + 2.1 + 0.0 + 20.5 + 5.3 + 1.0) ÷ 7 
= 41.1 ÷ 7 
= 5.87 mm. 
 
 
 
 
 
    
 
 
(iii) Clearly, there are 5 days (Mon, Wed, Thu, Sat and Sun), when the rainfall was less 
than the mean, i.e., 5.87 mm. 
 
6. If the heights of 5 persons are 140 cm, 150 cm, 152 cm, 158 cm and 161 cm 
respectively, find the mean height. 
 
Solution: 
The mean height = Sum of the heights /Total number of persons 
= (140 + 150 + 152 + 158 + 161) ÷ 5 
= 761 ÷ 5 
= 152.2 cm. 
 
7. Find the mean of 994, 996, 998, 1002 and 1000. 
 
Solution: 
Mean = Sum of the given numbers/Total number of given numbers 
Mean = (994 + 996 + 998 + 1002 + 1000) ÷ 5 
= 4990 ÷ 5 
= 998. 
 
8. Find the mean of first five natural numbers. 
 
Solution: 
We know that first five natural numbers = 1, 2, 3, 4 and 5 
Mean of first five natural numbers = (1 + 2 + 3 + 4 + 5) ÷ 5 
= 15 ÷ 5 
= 3 
 
9.  Find the mean of all factors of 10. 
 
Solution: 
We know that factors of 10 are 1, 2, 5 and 10 
Arithmetic mean of all factors of 10 = (1 + 2 + 5 + 10) ÷ 4 
= 18 ÷ 4 
= 4.5 
 
 
 
 
 
 
    
 
10. Find the mean of first 10 even natural numbers. 
 
Solution: 
The first 10 even natural numbers are 2, 4, 6, 8, 10, 12, 14, 16, 18 and 20. 
Mean of first 10 even natural numbers = (2 + 4 + 6 + 8 + 10 + 12 + 14 + 16 + 18 + 20) ÷ 10 
= 110 ÷ 10 
= 11 
 
11. Find the mean of x, x + 2, x + 4, x + 6, x + 8 
 
Solution: 
Mean = Sum of observations ÷ Number of observations 
Mean = (x + x + 2 + x + 4 + x + 6 + x + 8) ÷ 5 
Mean = (5x + 20) ÷ 5 
Mean = 5 (x + 4) ÷ 5 
Mean = x + 4 
 
12. Find the mean of first five multiples of 3. 
 
Solution: 
The first five multiples of 3 are 3, 6, 9, 12 and 15. 
Mean of first five multiples of 3 are = (3 + 6 + 9 + 12 + 15) ÷ 5 
= 45 ÷ 5 
= 9 
 
13. Following are the weights (in kg) of 10 new born babies in a hospital on a 
particular day: 3.4, 3.6, 4.2, 4.5, 3.9, 4.1, 3.8, 4.5, 4.4, 3.6 Find the mean  
 
Solution: 
We know that 
 = sum of observations/ number of observations  
= sum of weights of babies/ number of babies 
 = (3.4 + 3.6 + 4.2 + 4.5 + 3.9 + 4.1 + 3.8 + 4.5 + 4.4 + 3.6) ÷ 10 
 = (40) ÷ 10 
 = 4 kg 
 
14. The percentage of marks obtained by students of a class in mathematics are: 
Page 5


 
 
 
 
 
    
 
         
 
1. Ashish studies for 4 hours, 5 hours and 3 hours on three consecutive days. How 
many hours does he study daily on an average?  
 
Solution: 
Given Ashish studies for 4 hours, 5 hours and 3 hours on three consecutive days 
Average number of study hours = sum of hours/ number of days 
Average number of study hours = (4 + 5 + 3) ÷ 3 
= 12 ÷ 3 
= 4 hours 
Thus, Ashish studies for 4 hours on an average. 
 
2. A cricketer scores the following runs in 8 innings: 58, 76, 40, 35, 48, 45, 0, 100. 
Find the mean score. 
 
Solution: 
Given runs in 8 innings: 58, 76, 40, 35, 48, 45, 0, 100 
Mean score = total sum of runs/number of innings 
The mean score = (58 + 76 + 40 + 35 + 48 + 45 + 0 + 100) ÷ 8 
= 402 ÷ 8 
= 50.25 runs. 
 
3. The marks (out of 100) obtained by a group of students in science test are 85, 76, 
90, 84, 39, 48, 56, 95, 81 and 75. Find the 
(i) Highest and the lowest marks obtained by the students. 
(ii) Range of marks obtained. 
(iii) Mean marks obtained by the group. 
 
Solution: 
In order to find the highest and lowest marks, we have to arrange the marks in 
ascending order as follows: 
39, 48, 56, 75, 76, 81, 84, 85, 90, 95 
 
(i) Clearly, the highest mark is 95 and the lowest is 39. 
 
 
 
 
 
 
    
 
(ii) The range of the marks obtained is: (95 – 39) = 56. 
 
(iii) From the following data, we have 
Mean marks = Sum of the marks/ Total number of students 
Mean marks = (39 + 48 + 56 + 75 + 76 + 81 + 84 + 85 + 90 + 95) ÷ 10 
= 729 ÷ 10 
= 72.9. 
Hence, the mean mark of the students is 72.9. 
 
4. The enrolment of a school during six consecutive years was as follows: 
1555, 1670, 1750, 2019, 2540, 2820 
Find the mean enrolment of the school for this period. 
 
Solution: 
Given enrolment of a school during six consecutive years as follows  
1555, 1670, 1750, 2019, 2540, 2820 
The mean enrolment = Sum of the enrolments in each year/ Total number of years 
The mean enrolment = (1555 + 1670 + 1750 + 2019 + 2540 + 2820) ÷ 6 
= 12354 ÷ 6 
= 2059. 
Thus, the mean enrolment of the school for the given period is 2059. 
 
5. The rainfall (in mm) in a city on 7 days of a certain week was recorded as follows: 
Day Mon Tue Wed Thu Fri Sat Sun 
Rainfall (in mm) 0.0 12.2 2.1 0.0 20.5 5.3 1.0 
(i) Find the range of the rainfall from the above data. 
(ii) Find the mean rainfall for the week. 
(iii) On how many days was the rainfall less than the mean rainfall. 
 
Solution: 
(i) The range of the rainfall = Maximum rainfall – Minimum rainfall 
= 20.5 – 0.0 
= 20.5 mm. 
 
(ii) The mean rainfall = (0.0 + 12.2 + 2.1 + 0.0 + 20.5 + 5.3 + 1.0) ÷ 7 
= 41.1 ÷ 7 
= 5.87 mm. 
 
 
 
 
 
    
 
 
(iii) Clearly, there are 5 days (Mon, Wed, Thu, Sat and Sun), when the rainfall was less 
than the mean, i.e., 5.87 mm. 
 
6. If the heights of 5 persons are 140 cm, 150 cm, 152 cm, 158 cm and 161 cm 
respectively, find the mean height. 
 
Solution: 
The mean height = Sum of the heights /Total number of persons 
= (140 + 150 + 152 + 158 + 161) ÷ 5 
= 761 ÷ 5 
= 152.2 cm. 
 
7. Find the mean of 994, 996, 998, 1002 and 1000. 
 
Solution: 
Mean = Sum of the given numbers/Total number of given numbers 
Mean = (994 + 996 + 998 + 1002 + 1000) ÷ 5 
= 4990 ÷ 5 
= 998. 
 
8. Find the mean of first five natural numbers. 
 
Solution: 
We know that first five natural numbers = 1, 2, 3, 4 and 5 
Mean of first five natural numbers = (1 + 2 + 3 + 4 + 5) ÷ 5 
= 15 ÷ 5 
= 3 
 
9.  Find the mean of all factors of 10. 
 
Solution: 
We know that factors of 10 are 1, 2, 5 and 10 
Arithmetic mean of all factors of 10 = (1 + 2 + 5 + 10) ÷ 4 
= 18 ÷ 4 
= 4.5 
 
 
 
 
 
 
    
 
10. Find the mean of first 10 even natural numbers. 
 
Solution: 
The first 10 even natural numbers are 2, 4, 6, 8, 10, 12, 14, 16, 18 and 20. 
Mean of first 10 even natural numbers = (2 + 4 + 6 + 8 + 10 + 12 + 14 + 16 + 18 + 20) ÷ 10 
= 110 ÷ 10 
= 11 
 
11. Find the mean of x, x + 2, x + 4, x + 6, x + 8 
 
Solution: 
Mean = Sum of observations ÷ Number of observations 
Mean = (x + x + 2 + x + 4 + x + 6 + x + 8) ÷ 5 
Mean = (5x + 20) ÷ 5 
Mean = 5 (x + 4) ÷ 5 
Mean = x + 4 
 
12. Find the mean of first five multiples of 3. 
 
Solution: 
The first five multiples of 3 are 3, 6, 9, 12 and 15. 
Mean of first five multiples of 3 are = (3 + 6 + 9 + 12 + 15) ÷ 5 
= 45 ÷ 5 
= 9 
 
13. Following are the weights (in kg) of 10 new born babies in a hospital on a 
particular day: 3.4, 3.6, 4.2, 4.5, 3.9, 4.1, 3.8, 4.5, 4.4, 3.6 Find the mean  
 
Solution: 
We know that 
 = sum of observations/ number of observations  
= sum of weights of babies/ number of babies 
 = (3.4 + 3.6 + 4.2 + 4.5 + 3.9 + 4.1 + 3.8 + 4.5 + 4.4 + 3.6) ÷ 10 
 = (40) ÷ 10 
 = 4 kg 
 
14. The percentage of marks obtained by students of a class in mathematics are: 
 
 
 
 
 
    
 
64, 36, 47, 23, 0, 19, 81, 93, 72, 35, 3, 1 Find their mean. 
 
Solution: 
Mean = sum of the marks obtained/ total number of students 
= (64 + 36 + 47 + 23 + 0 + 19 + 81 + 93 + 72 + 35 + 3 + 1) ÷ 12 
= 474 ÷ 12 
= 39.5% 
 
15. The numbers of children in 10 families of a locality are: 
2, 4, 3, 4, 2, 3, 5, 1, 1, 5 Find the mean number of children per family. 
 
Solution: 
Mean number of children per family = sum of total number of children / total number of 
families 
= (2 + 4 + 3 + 4 + 2 + 3 + 5 + 1 + 1 + 5) ÷ 10 
= 30 ÷ 10 
= 3 
Thus, on an average there are 3 children per family in the locality. 
 
16. The mean of marks scored by 100 students was found to be 40. Later on it was 
discovered that a score of 53 was misread as 83. Find the correct mean. 
 
Solution: 
Given n = the number of observations = 100, Mean = 40 
Mean = sum of observations/total number of observations 
40 = sum of the observations/ 100 
Sum of the observations = 40 x 100 
Thus, the incorrect sum of the observations = 40 x 100 = 4000. 
Now, 
The correct sum of the observations = Incorrect sum of the observations – Incorrect 
observation + Correct observation 
The correct sum of the observations = 4000 – 83 + 53 
The correct sum of the observations = 4000 – 30 = 3970 
Correct mean = correct sum of the observations/ number of observations  
= 3970/100 
= 39.7