Find mean,mode and median of following.

Marks: Less than 30,40,50,60,70,80,90 (All less than )

No of students: 5,12,25,30,34,38,40

The data can be represented in the form of a table as shown below:



From the table above we can see that the 20th observation lies in the class interval 40-50 so the median class is 40-50.

Median=l+n2-cff×h=40+402-1213×10=40+8013=46.154

From the table it is clear that maximum frequency lies in the class interval 40-50. So, the modal class is 40-50.

Mode=l+f1-f02f1-f0-f2×h=40+13-72×13-7-5×10=40+6014=44.286

Now, consider the formula,
 
3Median = Mode + 2 Mean

Mean = 123Median-Mode=123×46.154-44.286=1294.176=47.088

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