Following are the marks of 30 students in a class  20, 22, 22, 25, 26, 26, 0, 10, 0, 25, 22, 23, 22, 24, 22, 24, 25, 23, 21, 25, 28, 29, 30, 27, 22, 24, 22, 25, 0, 10,

then the frequency of students having marks 22 is:

7

According to the above numbers, frequency of students having 22 marks is 7, which have been highlighted as follows:

20, 22, 22, 25, 26, 26, 0, 10, 0, 25, 22, 23, 22, 24, 22, 24, 25, 23, 21, 25, 28, 29, 30, 27, 22, 24, 22, 25, 0, 10.