find the sum of lower limit of modal class and median of the following data: 30-40......25, 40-50......30, 50-60...16, 60-70...19, 70-80....17, 80-90.....18 ?

Putting the given data in the form of a table:
Class Interval Frequency(f) Cumulative frequency (c.f)
30-40 25 25
40-50 30 55
50-60 16 71
60-70 19 90
70-80 17 107
80-90 18 125
Total   N=125

The modal group, i.e., the group with the highest frequency is 40-50.The lower limit of the modal group is 40.Also, N is the sum of all frequencies and N=125.Now, N+12=125+12=63. The cumulative frequency just greater than N+12=63is 71  and the corresponding group is 50-60. So, 50-60  is the median group.Lower limit of the median group is 50.The sum of lower limit of modal group and the lower limit of median group=40+50=90.

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