Question

A survey was conducted by a group of students as a part of their environment awareness programme, in which they collected the following data regarding the number of plants in 20 houses in a locality. Find the mean number of plants per house.

Number of plants	0­ − 2	2­ − 4	4 − 6	6 − 8	8 − 10	10 − 12	12 − 14
Number of houses	1	2	1	5	6	2	3

Which method did you use for finding the mean, and why?

Answer 1

To find the class mark (x_i) for each interval, the following relation is used.

Class mark (x_i) =

x_i and f_ix_i can be calculated as follows.

Number of plants	Number of houses (fi)	xi	fixi
0­ − 2	1	1	1 × 1 = 1
2­ − 4	2	3	2 × 3 = 6
4 − 6	1	5	1 × 5 = 5
6 − 8	5	7	5 × 7 = 35
8 − 10	6	9	6 × 9 = 54
10 − 12	2	11	2 ×11 = 22
12 − 14	3	13	3 × 13 = 39
Total	20		162

From the table, it can be observed that

Mean,

Therefore, mean number of plants per house is 8.1.

Here, direct method has been used as the values of class marks (x_i) and f_i are small.