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Question
The following table shows the weight of 12 students:
| Weight in kg. | 67 | 70 | 72 | 73 | 75 |
| Number of students | 4 | 3 | 2 | 2 | 1 |
Find the Mean weight.
Solution
Let the assumed mean A = 72. Calculate of Mean:
| Weight in kgs. | Number of students `(f_i)` | `d_i = x_i - A = x_i - 72` | `f_i d_i` |
| 67 | 4 | -5 | -20 |
| 70 | 3 | -2 | -6 |
| 72 | 2 | 0 | 0 |
| 73 | 2 | 1 | 2 |
| 75 | 1 | 3 | 3 |
| N = `sumf_i = 12` | `sumf_i d_i = -21` |
We have,
N = 12, E = `f_i d_i` = -21, A = 72
Mean = `"A" + (1)/"N" (sumf_i d_i)`
= `72 + (-21/12)`
= `72 - (7)/(4)`
= `(288 - 7)/(4)`
= `(2881)/(4)`
= 70·25 kgs.
∴ Mean weight = 70·25 kgs.
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