if in a row i have 11 students if within these students some missed class what formula can i use to get the number that missed class
You must have some identifier that indicates that a student missed class. You can then use that identifier to count the students who have missed. In your information you have indicated that the 11 students are in a row. I am not sure if they are in the same cell in the row, or different cells. Usually the list would not be in a row but in a column so I am going to assume that your list is in a column and give you an answer based on that.
Assume your list is in column A cell A1 to cell A11
If your put the criteria of absent or present next to the name, in column B, you can use a formula to count those that are absent. For example if the number one represents present and the number two represents absent, you can use this formula to count the absents =COUNTIF(B1:B11,2)
You can also use alpha as your criteria I.E. put in "Present" or "Absent" in column B next to each students name. In that case the formula would look like this =COUNTIF(B1:B11,"Absent")