Following are the marks obtained by 30 students in examinations.
15, 20, 8, 9, 10,
16, 17, 20, 24, 30,
44, 47, 38, 36, 40,
27, 25, 28, 30, 19,
7, 11, 21, 31, 41,
37, 47, 23, 20, 17
Taking class intervals 0-10, 10-20, ......... 40-50 ; construct a frequency table.