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.


Numbers of plants:



0-2



2-4



4-6



6-8



8-10



10-12



12-14



Numbers of houses:



1



2



1



5



6



2



3



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

Let us find class marks (xi) for each interval by using the relation.

Class mark (xi) =


Now we may compute xi and fixi as follows:


Number of plants



Number of house (fi)



xi



fixi



0 – 2



1



1



1



2 – 4



2



3



6



4 – 6



1



5



5



6 – 8



5



7



35



8 – 10



6



9



54



10 – 12



2



11



22



12 – 14



3



13



39




N = 20




∑fixi = 162



Fro, the table we may observe that,


∑fi = 20


∑fixi = 162


Mean, X̅ =


= = 8.1


So mean number of plants per house is 8.1


We have used for the direct method values xi and fi are very small.


2