|
Classes |
xi |
yi = (xi – 105)/30 |
f i |
f i y i |
f i y i2 |
|
0-30 |
15 |
-3 |
2 |
-6 |
18 |
|
30-60 |
45 |
-2 |
3 |
-6 |
12 |
|
60-90 |
75 |
-1 |
5 |
-5 |
5 |
|
90-120 |
105 |
0 |
10 |
0 |
0 |
|
120-150 |
135 |
1 |
3 |
3 |
3 |
|
150-180 |
165 |
2 |
5 |
10 |
20 |
|
180-210 |
195 |
3 |
2 |
6 |
18 |
|
Total |
30 |
2 |
76 |
=
= 107
Hence Variance (σ 2) = [(30)2/30][76 – 4/30] = 2276
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