问题1.下表列出了城市中体力劳动者的家庭总支出(以卢比计)的分布。
Expenditure (in rupees) (x) | Frequency (fi) | Expenditure (in rupees) (xi) | Frequency (fi) |
100 – 150 | 24 | 300 – 350 | 30 |
150 – 200 | 40 | 350 – 400 | 22 |
200 – 250 | 33 | 400 – 450 | 16 |
250 – 300 | 28 | 450 – 500 | 7 |
找出每个家庭的平均支出(以卢比为单位)。
解决方案:
Let the assumed mean (A) = 275
It’s seen that A = 275 and h = 50
So,
Mean = A + h x (Σfi ui/N)
= 275 + 50 (-35/200)
= 275 – 8.75
= 266.25
问题2。作为他们的环境意识计划的一部分,一群学生进行了一项调查,他们收集了以下有关本地200所房屋中植物数量的数据。找出每所房子的平均植物数量。
Class interval | Mid value (xi) | di = xi – 275 | ui = (xi – 275)/50 | Frequency fi | fiui |
100 – 150 | 125 | -150 | -3 | 24 | -72 |
150 – 200 | 175 | -100 | -2 | 40 | -80 |
200 – 250 | 225 | -50 | -1 | 33 | -33 |
250 – 300 | 275 | 0 | 0 | 28 | 0 |
300 – 350 | 325 | 50 | 1 | 30 | 30 |
350 – 400 | 375 | 100 | 2 | 22 | 44 |
400 – 450 | 425 | 150 | 3 | 16 | 48 |
450 – 500 | 475 | 200 | 4 | 7 | 28 |
N = 200 | Σ fiui = -35 |
您使用哪种方法求平均值,为什么?
解决方案:
From the given data,
To find the class interval we know that,
Class marks (xi) = (upper class limit + lower class limit)/2
Now, let’s compute xi and fixi by the following
Here,
Mean = Σ fiui/N
= 162/ 20
= 8.1
Thus, the mean number of plants in a house is 8.1
We have used the direct method as the values of class mark xi and fi is very small.
问题3.考虑以下工厂工人的日工资分配
Number of plants: | 0 – 2 | 2 – 4 | 4 – 6 | 6 – 8 | 8 – 10 | 10 – 12 | 12 – 14 |
Number of house: | 1 | 2 | 1 | 5 | 6 | 2 | 3 |
用适当的方法求出工厂工人的平均日工资。
解决方案:
Let us assume mean (A) = 150
It’s seen that,
A = 150 and h = 20
So,
Mean = A + h x (Σfi ui/N)
= 150 + 20 x (-12/50)
= 150 – 24/5
= 150 = 4.8
= 145.20
问题4。30名妇女在医院接受了医生检查,每分钟的心跳数记录并总结如下。选择合适的方法,找出这些女性每分钟的平均心跳数。
Number of plants | Number of house (fi) | xi | fixi |
0 – 2 | 1 | 1 | 1 |
2 – 4 | 2 | 3 | 6 |
4 – 6 | 1 | 5 | 5 |
6 – 8 | 5 | 7 | 35 |
8 – 10 | 6 | 9 | 54 |
10 – 12 | 2 | 11 | 22 |
12 – 14 | 3 | 13 | 39 |
Total | N = 20 | Σ fiui = 162 |
解决方案:
Using the relation (xi) = (upper class limit + lower class limit)/ 2
And, class size of this data = 3
Let the assumed mean (A) = 75.5
So, let’s calculate di, ui, fiui as following:
From table, it’s seen that
N = 30 and h = 3
So, the mean = A + h x (Σfi ui/N)
= 75.5 + 3 x (4/30
= 75.5 + 2/5
= 75.9
Therefore, the mean heart beats per minute for those women are 75.9 beats per minute.
问题5.找到以下每个频率分布的均值:
Daily wages (in ₹) | 100 – 120 | 120 – 140 | 140 – 160 | 160 – 180 | 180 – 200 |
Number of workers: | 12 | 14 | 8 | 6 | 10 |
解决方案:
Let’s consider the assumed mean (A) = 15
From the table it’s seen that,
A = 15 and h = 6
Mean = A + h x (Σfi ui/N)
= 15 + 6 x (3/40)
= 15 + 0.45
= 15.45
问题6.找到以下频率分布的均值:
Class interval | Mid value xi | di = xi – 150 | ui = (xi – 150)/20 | Frequency fi | fiui |
100 – 120 | 110 | -40 | -2 | 12 | -24 |
120 – 140 | 130 | -20 | -1 | 14 | -14 |
140 – 160 | 150 | 0 | 0 | 8 | 0 |
160 – 180 | 170 | 20 | 1 | 6 | 6 |
180 – 200 | 190 | 40 | 2 | 10 | 20 |
N= 50 | Σ fiui = -12 |
解决方案:
Let’s consider the assumed mean (A) = 100
From the table it’s seen that,
A = 100 and h = 20
Mean = A + h x (Σfi ui/N)
= 100 + 20 x (61/100)
= 100 + 12.2
= 112.2
问题7:找到以下频率分布的均值:
Number of heart beats per minute: | 65 – 68 | 68 – 71 | 71 – 74 | 74 – 77 | 77 – 80 | 80 – 83 | 83 – 86 |
Number of women: | 2 | 4 | 3 | 8 | 7 | 4 | 2 |
解决方案:
From the table it’s seen that,
A = 20 and h = 8
Mean = A + h x (Σfi ui/N)
= 20 + 8 x (7/40)
= 20 + 1.4
= 21.4
问题8:找到以下频率分布的均值:
Number of heart beats per minute | Number of women (fi) | xi | di = xi – 75.5 | ui = (xi – 755)/h | fiui |
65 – 68 | 2 | 66.5 | -9 | -3 | -6 |
68 – 71 | 4 | 69.5 | -6 | -2 | -8 |
71 – 74 | 3 | 72.5 | -3 | -1 | -3 |
74 – 77 | 8 | 75.5 | 0 | 0 | 0 |
77 – 80 | 7 | 78.5 | 3 | 1 | 7 |
80 – 83 | 4 | 81.5 | 6 | 2 | 8 |
83 – 86 | 2 | 84.5 | 9 | 3 | 6 |
N = 30 | Σ fiui = 4 |
解决方案:
Let’s consider the assumed mean (A) = 15
Class interval | Mid – value xi | di = xi – 15 | ui = (xi – 15)/6 | fi | fiui |
0 – 6 | 3 | -12 | -2 | 7 | -14 |
6 – 12 | 9 | -6 | -1 | 5 | -5 |
12 – 18 | 15 | 0 | 0 | 10 | 0 |
18 – 24 | 21 | 6 | 1 | 12 | 12 |
24 – 30 | 27 | 12 | 2 | 6 | 12 |
N = 40 | Σ fiui = 5 |
From the table it’s seen that,
A = 15 and h = 6
Mean = A + h x (Σfi ui/N)
= 15 + 6 x (5/40)
= 15 + 0.75
= 15.75
问题9.找到以下频率分布的均值:
Class interval: | 0 – 6 | 6 – 12 | 12 – 18 | 18 – 24 | 24 – 30 |
Frequency: | 6 | 8 | 10 | 9 | 7 |
解决方案:
Let’s consider the assumed mean (A) = 25
Class interval | Mid – value xi | di = xi – 25 | ui = (xi – 25)/10 | fi | fiui |
0 – 10 | 5 | -20 | -2 | 9 | -18 |
10 – 20 | 15 | -10 | -1 | 12 | -12 |
20 – 30 | 25 | 0 | 0 | 15 | 0 |
30 – 40 | 35 | 10 | 1 | 10 | 10 |
40 – 50 | 45 | 20 | 2 | 14 | 28 |
N = 60 | Σ fiui = 8 |
From the table it’s seen that,
A = 25 and h = 10
Mean = A + h x (Σfi ui/N)
= 25 + 10 x (8/60)
= 25 + 4/3
= 79/3 = 26.333
问题10:找到以下频率分布的均值:
Class interval | Mid – value xi | di = xi – 15 | ui = (xi – 15)/6 | fi | fiui |
0 – 6 | 3 | -12 | -2 | 6 | -12 |
6 – 12 | 9 | -6 | -1 | 8 | -8 |
12 – 18 | 15 | 0 | 0 | 10 | 0 |
18 – 24 | 21 | 6 | 1 | 9 | 9 |
24 – 30 | 27 | 12 | 2 | 7 | 14 |
N = 40 | Σ fiui = 3 |
解决方案:
Let’s consider the assumed mean (A) = 20
Class interval | Mid – value xi | di = xi – 20 | ui = (xi – 20)/8 | fi | fiui |
0 – 8 | 4 | -16 | -2 | 5 | -10 |
8 – 16 | 12 | -4 | -1 | 9 | -9 |
16 – 24 | 20 | 0 | 0 | 10 | 0 |
24 – 32 | 28 | 4 | 1 | 8 | 8 |
32 – 40 | 36 | 16 | 2 | 8 | 16 |
N = 40 | Σ fiui = 5 |
From the table it’s seen that,
A = 20 and h = 8
Mean = A + h x (Σfi ui/N)
= 20 + 8 x (5/40)
= 20 + 1
= 21
问题11:找到以下频率分布的均值:
Class interval: | 50 – 70 | 70 – 90 | 90 – 110 | 110 – 130 | 130 – 150 | 150 – 170 |
Frequency: | 18 | 12 | 13 | 27 | 8 | 22 |
解决方案:
Let’s consider the assumed mean (A) = 20
Class interval | Mid – value xi | di = xi – 20 | ui = (xi – 20)/8 | fi | fiui |
0 – 8 | 4 | -16 | -2 | 5 | -12 |
8 – 16 | 12 | -8 | -1 | 6 | -8 |
16 – 24 | 20 | 0 | 0 | 4 | 0 |
24 – 32 | 28 | 8 | 1 | 3 | 9 |
32 – 40 | 36 | 16 | 2 | 2 | 14 |
N = 20 | Σ fiui = -9 |
From the table it’s seen that,
A = 20 and h = 8
Mean = A + h x (Σfi ui/N)
= 20 + 6 x (-9/20)
= 20 – 72/20
= 20 – 3.6
= 16.4
问题12:找到以下频率分布的均值:
Class interval | Mid – value xi | di = xi – 100 | ui = (xi – 100)/20 | fi | fiui |
50 – 70 | 60 | -40 | -2 | 18 | -36 |
70 – 90 | 80 | -20 | -1 | 12 | -12 |
90 – 110 | 100 | 0 | 0 | 13 | 0 |
110 – 130 | 120 | 20 | 1 | 27 | 27 |
130 – 150 | 140 | 40 | 2 | 8 | 16 |
150 – 170 | 160 | 60 | 3 | 22 | 66 |
N= 100 | Σ fiui = 61 |
解决方案:
Let’s consider the assumed mean (A) = 60
Class interval | Mid – value xi | di = xi –60 | ui = (xi – 60)/20 | fi | fiui |
10 – 30 | 20 | -40 | -2 | 5 | -10 |
30 – 50 | 40 | -20 | -1 | 8 | -8 |
50 – 70 | 60 | 0 | 0 | 12 | 0 |
70 – 90 | 80 | 20 | 1 | 20 | 20 |
90 – 110 | 100 | 40 | 2 | 3 | 6 |
110 – 130 | 120 | 60 | 3 | 2 | 6 |
N = 50 | Σ fiui = 14 |
From the table it’s seen that,
A = 60 and h = 20
Mean = A + h x (Σfi ui/N)
= 60 + 20 x (14/50)
= 60 + 28/5
= 60 + 5.6
= 65.6
问题13:找到以下频率分布的均值:
Class interval: | 0 – 8 | 8 – 16 | 16 – 24 | 24 – 32 | 32 – 40 |
Frequency: | 6 | 7 | 10 | 8 | 9 |
解决方案:
Let’s consider the assumed mean (A) = 50
Class interval | Mid – value xi | di = xi – 50 | ui = (xi – 50)/10 | fi | fiui |
25 – 35 | 30 | -20 | -2 | 6 | -12 |
35 – 45 | 40 | -10 | -1 | 10 | -10 |
45 – 55 | 50 | 0 | 0 | 8 | 0 |
55 – 65 | 60 | 10 | 1 | 12 | 12 |
65 – 75 | 70 | 20 | 2 | 4 | 8 |
N = 40 | Σ fiui = -2 |
From the table it’s seen that,
A = 50 and h = 10
Mean = A + h x (Σfi ui/N)
= 50 + 10 x (-2/40)
= 50 – 0.5
= 49.5