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The following distribution shows the daily pocket allowance of children of a locality. The mean pocket allowance is Rs 18. Find the missing frequency
To find the class mark (xi) for each interval, the following relation is used.
Given that, mean pocket allowance, 
Taking 18 as assured mean (a), di and fidi are calculated as follows.
From the table, we obtain
Hence, the missing frequency, f, is 20.
Consider the following distribution of daily wages of 50 workers of a factory.
Find the mean daily wages of the workers of the factory by using an appropriate method.
To find the class mark for each interval, the following relation is used.
Class size (h) of this data = 20
Taking 550 as assured mean (a), di, ui, and fiui can be calculated as follows.
From the table, it can be observed that
= 545.2
Therefore, the mean daily wage of the workers of the factory is Rs 545.20.
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.
Which method did you use for finding the mean, and why?
To find the class mark (xi) for each interval, the following relation is used.
Class mark (xi) = 
xi and fixi can be calculated as follows.
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 (xi) and fi are small.
Thirty women were examined in a hospital by a doctor and the number of heartbeats per minute were recorded and summarised as follows. Find the mean heartbeats per minute for these women, choosing a suitable method.
To find the class mark of each interval (xi), the following relation is used.
Class size, h, of this data = 3
Taking 75.5 as assumed mean (a), di, ui, fiui are calculated as follows.
From the table, we obtain
Therefore, mean hear beats per minute for these women are 75.9 beats per minute.
In a retail market, fruit vendors were selling mangoes kept in packing boxes. These boxes contained varying number of mangoes. The following was the distribution of mangoes according to the number of boxes.
Find the mean number of mangoes kept in a packing box. Which method of finding the mean did you choose?
It can be observed that class intervals are not continuous. There is a gap of 1 between two class intervals. Therefore,
has to be added to the upper class limit and has to be subtracted from the lower class limit of each interval.
Class mark (xi) can be obtained by using the following relation.
Class size (h) of this data = 3
Taking 57 as assumed mean (a), di, ui, fiui are calculated as follows.
It can be observed that
Mean number of mangoes kept in a packing box is 57.19.
Step deviation method is used here as the values of fi, di are big and also, there is a common multiple between all di.
The table below shows the daily expenditure on food of 25 households in a locality.
Find the mean daily expenditure on food by a suitable method.
To find the class mark (xi) for each interval, the following relation is used.
Class size = 50
Taking 225 as assumed mean (a), di, ui, fiui are calculated as follows.
From the table, we obtain
Therefore, mean daily expenditure on food is Rs 211.
To find out the concentration of in the air (in parts per million, i.e., ppm), the data was collected for 30 localities in a certain city and is presented below:
Find the mean concentration of in the air.
To find the class marks for each interval, the following relation is used.
Class size of this data = 0.04
Taking 0.14 as assumed mean (a), di, ui, fiui are calculated as follows.
From the table, we obtain
Therefore, mean concentration of SO2 in the air is 0.099 ppm.
A class teacher has the following absentee record of 40 students of a class for the whole term. Find the mean number of days a student was absent.
To find the class mark of each interval, the following relation is used.
Taking 17 as assumed mean (a), di and fidi are calculated as follows.
From the table, we obtain
Therefore, the mean number of days is 12.48 days for which a student was absent.
The following table gives the literacy rate (in percentage) of 35 cities. Find the mean literacy rate.
To find the class marks, the following relation is used.
Class size (h) for this data = 10
Taking 70 as assumed mean (a), di, ui, and fiui are calculated as follows.
From the table, we obtain
Therefore, mean literacy rate is 69.43%.
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