Question

Write the formula for mean for a grouped data. Explain the terms of it.

Answer 1

I think sum of observations/No.of observations

Answer 2

The mean of the grouped data can be found in the following way -

1) Determine the midpoints for each class i.e. find out the class mark

Take the Lower Limit of the class and the Upper Limit of the class and add then and divide the product by 2 - do this for all the classes.

Example: 0 - 10 is the class given to me

10 + 0 = 10 / 2 = 5 (Class Mark / Midpoint is 5 for the class 0 - 10)

2) Now, the midpoints that you have gathered need to be multiplied by the frequency for each particular class

So Mean = 100/10 = 10. You can even compress this into the form of one table to ease your process.

Example: 0 - 10 with frequency 5 is the given class so -

If the midpoint if 5, multiply it by 5 and you get 5x5 = 25.

Do this for all the classes.

3) Divide the sum (add all the values of Step 2 and find out the sum) of the multiplied midpoints with the total frequency of the entire frequency table.

So, if the sum of all the multiplied midpoints by frequency is hundred and the total frequency is 10.

Here we go,

Mean = 100/10 = 10

You can even combine this into a table for easy understanding.