The mean of the following frequency distribution is 18. The frequency f
the class interval 19 - 21 is missing. Determine f.
Class interval 11 - 13 13 - 15 15 - 17 17 - 19 19-21 21 – 23 23 - 25
Frequency 3 6 9 13 f 5 41
OR
Answers
Answer:
Missing frequency f = 8
Step-by-step explanation:
We are given the following frequency distribution;
Class Interval Frequency (f) X X*f
11 - 13 3 12 36
13 - 15 6 14 84
15 - 17 9 16 144
17 - 19 13 18 234
19 - 21 f 20 20*f
21 - 23 5 22 110
23 - 25 4 24 96
∑f = 40+f ∑X*f = 704+20*f
Mean of the data, X bar =
18 =
18(40 + f) = 704 + 20*f
20*f - 18*f = 720 - 704
2*f = 16
f = 8
Therefore, missing frequency of class interval 19 - 21 is 8 .
Answer:
∑f=40+f ∑fx=704+20f
Given : Mean =18
⟹18(40+f)=704+20f
⟹720+18f=704+20f
⟹720−704=20f−18f
⟹2f=16
⟹f=8