This question was reported to be very popular among the candidates and their performance was commended. However, it was also observed that some candidates did not use the assumed mean as demanded by the rubrics of the paper.
Candidates were expected to obtain the following table.
Ages |
F |
X |
d |
fd |
d2 |
fd2 |
15 - 19 |
5 |
17 |
-25 |
-125 |
625 |
3125 |
20 - 24 |
22 |
22 |
-20 |
-440 |
400 |
8800 |
25 - 29 |
30 |
27 |
-15 |
-450 |
225 |
6750 |
30 - 34 |
32 |
32 |
-10 |
-320 |
100 |
3200 |
35 - 39 |
25 |
37 |
-5 |
-125 |
25 |
625 |
40 - 44 |
36 |
42 |
0 |
0 |
0 |
0 |
45 - 49 |
32 |
47 |
5 |
160 |
25 |
800 |
50 - 54 |
30 |
52 |
10 |
300 |
100 |
3000 |
55 - 59 |
21 |
57 |
15 |
315 |
225 |
4725 |
60- 64 |
2 |
62 |
20 |
40 |
400 |
800 |
|
∑f = 235 |
|
|
∑fd = -645 |
|
∑fd2 = 31825 |
Using the table, the mean was calculated using the formula, mean = A + , where A = Assumed mean = 42 i.e. Mean = 42 - = 42 – 2.74 = 39.26
Variance was obtained by applying the formula – = – ( = 127.89.