Question

 In the formula 

`overlineX``\[= a + \frac{\Sigma f_i d_i}{\Sigma f_i}\], for finding the mean of grouped data \[{d_i}^{'^s}\]   are derivations from \[a\] of

Options

• lower limits of classes

• upper limits ofclasses   

•  mid-points of classes    

•  frequency of the class marks 

Answer 1

The given formula represents the formula to find the mean by assumed mean method.
Here, d_i = \[x_i - a\]

 where x_i is the ith observation and a is assumed mean. 
So, d_i's are the deviation from a of mid-points of the classes.