## 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 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

 Class Interval Frequency Class Mark fixi 0 – 9 11  10 – 19 7  20 – 29 9  30 – 39 5  40 – 49 8     Mean =