Data collection Grouped Mean

Let n observation be x1, x2……….xn and their frequencies be f1, f2, f3…….fn respectively. We define the mean as

Mean =


is the Greek letter Sigma and shows Summation. While represents the mean

Example : 12

Find the mean of the following.

xi

10

15

20

25

30

35

40

fi

4

6

8

18

6

5

3

Solution:

We will rewrite the table in the following form.

  

Mean of Group Data

If a class interval is given we take the xi value as the class mark value and use the same formula

Example : 13

The table shows the weight or 50 persons in a group.

Weight in Kg

40 - 43

44 - 47

48 - 51

52 - 55

56 - 59

Number of persons

8

12

9

16

5

Find the mean weight.

Solution :

Weight in kg

Frequency fi

Class Mark

fi xi

40 – 43

8

44 – 47

12

48 – 51

9

52 – 55

16

56 – 59

5

 

50

 

 2467


Try these problems

The age of 50 players in a school are given below.

Age (in years)

14

15

16

17

Number of players

16

14

12

8


Answer:

i)   Find the mean of the following grouped frequency distribution.

Class interval

0 -9

10 - 19

20 –29

30 - 39

40 - 49

Frequency

11

7

9

5

8


Answer :

Class Interval

Frequency

Class Mark

fixi

0 – 9

11

10 – 19

7

20 – 29

9

30 – 39

5

40 – 49

8

 

 


Mean =