Find out the mode of the following marks obtained by 15 students in a class:

Marks: 4, 6, 5, 7, 9, 8, 10, 4, 7, 6, 5, 9, 8, 7, 7.

The blood groups of 30 students of class VIII are recoded as follows:

A, B, O, O, AB, O, A, O, B, A, O, B, A, O, O, A, AB, O, A, A, O, O, AB, B, A, O, B, A, B, O

Represent this data in the form of a frequency distribution table. Find out which is the most common and which is the rarest blood group among these students.

Thirty children were asked about the number of hours they watched T.V. programmes in the previous week. The results were found as follows:

1, 6, 2, 3, 5, 12, 5, 8, 4, 8, 10, 3, 4, 12, 2, 8, 15, 1, 17, 6, 3, 2, 8, 5, 9, 6, 8, 7, 14, 12

(i) Make a grouped frequency distribution table for this data, taking class width 5 and one of the class intervals as 5-10.

(ii) How many children watched television for 15 or more hours a week?

Given below are the cumulative frequencies showing the weights of 685 students of a school. Prepare a frequency distribution table.

Following are the ages of 360 patients getting medical treatment in a hospital on a day:

Construct a cumulative frequency distribution.