if the arithmetic mean of the data given below is 28 ,find out the missing frequency

x

0-9

10-19

20-29

30-39

40-49

50-59

f

12

18

27

?

17

6

x

f

Mid Values

(m)

fm

0-9

12

4.5

54

10-19

18

14.5

261

20-29

27

24.5

661.5

30-39

a

34.5

34.5a

40-49

17

44.5

756.5

50-59

6

54.5

327

Total

80 + a


 

2060 + 34.5a

In case of arithmetic mean, we do not need to convert the given inclusive series into exclusive series. So, we take them as it is.

Now, we are given, arithmetic mean as 28. Also, let us name the missing frequency as a.

We know,

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