Q2 of 141 Page 7

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.


More from this chapter

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9

Find the mean from the following frequency distribution of marks at a test in statistics:





























Marks (x):



5



10



15



20



25



30



35



40



45



50



No. of students (f):



15



50



80



76



72



45



39



9



8



6


 1

The following table gives the distribution of total household expenditure (in rupees) of manual workers in a city.

































Expenditure (in rupees) (in rupees)



Frequency (f)



Expenditure (in rupees) (x)



Frequency (f)



100-150



24



300-350



30



150-200



40



350-400



22



200-250



33



400-450



16



250-300



28



450-500



7



Find the average expenditure (in rupees) per household.

 3

Consider the following distribution of daily wages of 50 workers of a factory.



















Daily wages (in Rs):



100-120



120-140



140-160



160-180



180-200



Numbers of workers:



12



14



8



6



10



Find the mean daily wages of the workers of the factory by using an appropriate method.

 4

Thirty women were examined in a hospital by a doctor and the number of heart beats per minute recorded and summarized as follows. Find the mean heart beats per minute for these women, choosing a suitable method.























Number of heart beats per minute:



65-68



68-71



71-74



74-77



77-80



80-83



83-86



Number of women:



2



4



3



8



7



4



2



Find the mean of each of the following frequency distributions: (5-14)