Question

Calculate the missing frequency from the following data, when the mean is 33 : X : 5 , 15 , 25 , 35 , 45 , 55 F : 5 , 10 , 25 , 30 , ? , 10

Answer 1

The missing frequency is 20.

Given,

Data with class and frequency as X : 5 , 15 , 25 , 35 , 45 , 55 F : 5 , 10 , 25 , 30 , ? , 10.

The mean of the data is 33.

To Find,

The value of the missing frequency.

Solution,

The formula for calculating the mean is

Mean = Σfixi/Σfi, where fi is the frequency and xi is the class.

So, let us assume the missing frequency to be a.

Σfixi = 5(5)+15(10)+25(25)+35(30)+45a+55(10) = 2400+45a

Σfi = 5+10+25+30+a+10 = 80+a

So, substituting the values

Mean = 33

(2400+45a)/(80+a) = 33

2400+45a = 2640+33a

12a = 240

a = 240/12 = 20

Hence, the missing frequency is 20.

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