Krishna
0

Step 1:  Recall the formula of the mean of the grouped data

            NOTE: The mean (or average) of observations is the sum of the values of

            all the observations divided by the total number of observations.

          

            Let x_1, x_2, x_3............, x_n be observations with respective

            frequencies f_1, f_2,............f_n


                     Mean = \frac{f_1x_1 + f_2x_2 + ........f_nx_n}{f_1 + f_2 +..........+ f_n}


                                    or


                         Mean = \frac{\Sigma f_ix_i}{\Sigma f_i}


Step 2: Re-organize given data in the table and find the sum of all observations.

                


             Sum of the values of all the observations \Sigma f_ix_i = 499


               Total number of observations \Sigma f_i = 40


                   So, the mean = \frac{499}{40}


                         Mean = 12.4