NCERT Solutions for Class 11 Maths Chapter 15 – Statistics Ex 15.3
Question 1:
From the data given below state which group is more variable, A or B?
Marks
|
10-20
|
20-30
|
30-40
|
40-50
|
50-60
|
60-70
|
70-80
|
Group A
|
9
|
17
|
32
|
33
|
40
|
10
|
9
|
Group B
|
10
|
20
|
30
|
25
|
43
|
15
|
7
|
Answer:
Firstly, the standard deviation of group A is calculated as follows.
Marks
|
Group A
fi
|
Mid-point
xi
|
yi2
|
fiyi
|
fiyi2
| |
10-20
|
9
|
15
|
–3
|
9
|
–27
|
81
|
20-30
|
17
|
25
|
–2
|
4
|
–34
|
68
|
30-40
|
32
|
35
|
–1
|
1
|
–32
|
32
|
40-50
|
33
|
45
|
0
|
0
|
0
|
0
|
50-60
|
40
|
55
|
1
|
1
|
40
|
40
|
60-70
|
10
|
65
|
2
|
4
|
20
|
40
|
70-80
|
9
|
75
|
3
|
9
|
27
|
81
|
| Σ |
150
|
–6
|
342
|
Here, h = 10, N = 150, A = 45
The standard deviation of group B is calculated as follows.
- MarksGroup BfiMid-pointxiyi2fiyifiyi210-201015–39–309020-302025–24–408030-403035–11–303040-502545000050-60435511434360-70156524306070-80775392163
Σ 150–6366
Since the mean of both the groups is same, the group with greater standard deviation will be more variable.
Thus, group B has more variability in the marks.
Question 2:
From the prices of shares X and Y below, find out which is more stable in value:
X
|
35
|
54
|
52
|
53
|
56
|
58
|
52
|
50
|
51
|
49
|
Y
|
108
|
107
|
105
|
105
|
106
|
107
|
104
|
103
|
104
|
101
|
Answer:
The prices of the shares X are
35, 54, 52, 53, 56, 58, 52, 50, 51, 49
Here, the number of observations, N = 10
The following table is obtained corresponding to shares X.
xi
|  |  |
35
|
–16
|
256
|
54
|
3
|
9
|
52
|
1
|
1
|
53
|
2
|
4
|
56
|
5
|
25
|
58
|
7
|
49
|
52
|
1
|
1
|
50
|
–1
|
1
|
51
|
0
|
0
|
49
|
–2
|
4
|
350
|
The prices of share Y are
108, 107, 105, 105, 106, 107, 104, 103, 104, 101
The following table is obtained corresponding to shares Y.
yi
|  |  |
108
|
3
|
9
|
107
|
2
|
4
|
| 105 |
0
|
0
|
105
|
0
|
0
|
106
|
1
|
1
|
107
|
2
|
4
|
104
|
–1
|
1
|
103
|
–2
|
4
|
104
|
–1
|
1
|
101
|
–4
|
16
|
40
|
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C.V. of prices of shares X is greater than the C.V. of prices of shares Y.
Thus, the prices of shares Y are more stable than the prices of shares X.
Question 3:
An analysis of monthly wages paid to workers in two firms A and B, belonging to the same industry, gives the following results:
Firm A
|
Firm B
| |
No. of wage earners
|
586
|
648
|
Mean of monthly wages
|
Rs 5253
|
Rs 5253
|
Variance of the distribution of wages
|
100
|
121
|
(i) Which firm A or B pays larger amount as monthly wages?
(ii) Which firm, A or B, shows greater variability in individual wages?
Answer:
(i) Monthly wages of firm A = Rs 5253
Number of wage earners in firm A = 586
∴Total amount paid = Rs 5253 × 586
Monthly wages of firm B = Rs 5253
Number of wage earners in firm B = 648
∴Total amount paid = Rs 5253 × 648
Thus, firm B pays the larger amount as monthly wages as the number of wage earners in firm B are more than the number of wage earners in firm A.
(ii) Variance of the distribution of wages in firm A
= 100
= 100
∴ Standard deviation of the distribution of wages in firm
A ((σ1) = 
Variance of the distribution of wages in firm 
= 121
= 121
∴ Standard deviation of the distribution of wages in firm 
The mean of monthly wages of both the firms is same i.e., 5253. Therefore, the firm with greater standard deviation will have more variability.
Thus, firm B has greater variability in the individual wages.
Page No 376:
Question 4:
The following is the record of goals scored by team A in a football session:
No. of goals scored
|
0
|
1
|
2
|
3
|
4
|
No. of matches
|
1
|
9
|
7
|
5
|
3
|
For the team B, mean number of goals scored per match was 2 with a standard
deviation 1.25 goals. Find which team may be considered more consistent?
Answer:
The mean and the standard deviation of goals scored by team A are calculated as follows.
No. of goals scored
|
No. of matches
|
fixi
|
xi2
|
fixi2
|
0
|
1
|
0
|
0
|
0
|
1
|
9
|
9
|
1
|
9
|
2
|
7
|
14
|
4
|
28
|
3
|
5
|
15
|
9
|
45
|
4
|
3
|
12
|
16
|
48
|
25
|
50
|
130
|
Thus, the mean of both the teams is same.
The standard deviation of team B is 1.25 goals.
The average number of goals scored by both the teams is same i.e., 2. Therefore, the team with lower standard deviation will be more consistent.
Thus, team A is more consistent than team B.
Question 5:
The sum and sum of squares corresponding to length x (in cm) and weight y
(in gm) of 50 plant products are given below:
Which is more varying, the length or weight?
Answer:
Here, N = 50
∴ Mean, 
Mean, 
Thus, C.V. of weights is greater than the C.V. of lengths. Therefore, weights vary more than the lengths.
