|
Classes |
xi |
yi = (xi - 25)/10 |
f i |
f i y i |
f i y i2 |
|
0-10 |
5 |
-2 |
5 |
-10 |
20 |
|
10-20 |
15 |
-1 |
8 |
-8 |
8 |
|
20-30 |
25 |
0 |
15 |
0 |
0 |
|
30-40 |
35 |
1 |
16 |
16 |
16 |
|
40-50 |
45 |
2 |
6 |
12 |
24 |
|
Total |
50 |
10 |
68 |
=
= 27
Hence Variance (σ 2) = [(10)2/50][68 - 100/50] = 132
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