SOLUTION: Find out arithmetic mean from the following data by step deviation method: Marks |Frequency 12.5-17.5 | 4 17.5-22.5 | 20 22.5-27.5 | 17 27.5-32.5 | 15 32.5-37.5 | 2 37.5

Algebra ->  Statistics  -> Describing-distributions-with-numbers -> SOLUTION: Find out arithmetic mean from the following data by step deviation method: Marks |Frequency 12.5-17.5 | 4 17.5-22.5 | 20 22.5-27.5 | 17 27.5-32.5 | 15 32.5-37.5 | 2 37.5      Log On


   



Question 1039303: Find out arithmetic mean from the following data by step deviation method:
Marks |Frequency
12.5-17.5 | 4
17.5-22.5 | 20
22.5-27.5 | 17
27.5-32.5 | 15
32.5-37.5 | 2
37.5-42.5 | 5
42.5-47.5 | 5
47.5-52.5 | 2

Answer by robertb(5830) About Me  (Show Source):
You can put this solution on YOUR website!
Let the class interval 27.5 - 32.5 be the zero basis for the step deviation.
Note that the class mark for the basis class interval is 30, and the class width is 5.
d | f | df
----------------
-3 | 4 | -12
-2 | 20 | -40
-1 | 17 | -17
0 | 15 | 0
1 | 2 | 2
2 | 5 | 10
3 | 5 | 15
4 | 2 | 8
----------------
| 70 |-34
==> Mean = 30%2Bsum%28df%2C+i=1%2C8%29%2FN+=+30+%2B+%28-34%2F70%29%2A5+=+193%2F7, or about 27.57.