Let the assumed mean (A) be 100.
Class interval |
Mid value (xi) |
di = xi - 100 |
ui = \(\frac{xi-100}{20}\) |
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 |
\(\sum\)fiui = 61 |
A = 100, h = 20
Mean = A + h x \(\frac{\sum f_iu_i}{N}\)
\(=100+20\times\frac{61}{100}\)
\(=100\,+12.2\)
\(=112.2\)