Question

Could someone pls help me with the first question ???

Answer 1

At first u should have to find class intervals
follows as 40-60
60-70
70-75
75-90
and the by using mean method we can get the respective answer

Answer 2

mid interval values=1/2(lower limit +upper limit)
 
mid values of time intervals x   50;  65;  72.5;   82.5
                                             f   10;  50;   80;      60

                                         f*x=500  3250   5800   4950
                                      
                             mean= sum of fx/sum of f  =14500/200
                                                                        = 72.5