5. While computing mean of grouped data, we assume that the frequencies are
(a) evenly distributed over all the classes (b) centred at the classmarks of the classes
(c) centred at the upper limits of the classes (d) centred at the lower limits of the classes
Answers
Given : A class teacher has the following record of marks obtained by 50 students of his class
Marks obtained 0-20 20-40 40-60 60 - 80 80 - 100
No of students 5 12 20 10 3
To Find : While computing mean of grouped data we assume that the frequencies are:
i) evenly distributed over all the classes
ii)centred at the lower limits of the classes
iii)centred at the classmarks of the classes
iv) centred at the upper limit of the classes
What will be the upper limit of the modal;
How many students have obtained more than 60 marks?
Solution :
While computing mean of grouped data we assume that the frequencies are: centred at the classmarks of the classes
classmarks = ( lower limit + upper limit )/2
Marks obtained f
0-20 5
20-40 12
40-60 20
60 - 80 10
80 - 100 3
20 is the highest frequency hence modal class is
40 - 60
upper limit of the modal = 60
students have obtained more than 60 marks
60 - 80 and 80 - 100
= 10 + 3 = 13
13 students have obtained more than 60 marks
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