If the mean of the following data is 4, find the missing frequency.

X	3	5	9	2
F	3	4	-	8

find the missing value.

Correct option is D

Given: 

Mean = 4

X given as 3, 5, 9, and 2

F given as 3, 4, and 8, with one frequency missing '$$f$$'

Formula used:

​$$\text{Mean} = \frac{\sum (X \cdot F)}{\sum F}$$ 

Solution:

Let the missing frequency be $$f$$​.

The formula for the mean:

$$4 = \frac{(3 \cdot 3) + (5 \cdot 4) + (9 \cdot f) + (2 \cdot 8)}{3 + 4 + f + 8}$$ 

 $$4 = \frac{9 + 20 + 9f + 16}{15 + f}$$

60 + 4f = 45 + 9f 

​$$f$$ = 3 

Thus the missing frequency f = 3

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