I have a list of students
S1
S2
S3

each has a row of errors##
S1 3.1, 3.3, 6.1
S2 6.1, 12.1
S3 3.3, 6.1, 11.1
S4

I want to be able to predict the possible errors in S4, so I want the common errors that appear in all the others. In this case above 3.3, 6.1

so S4 becomes 3.3, 6.1

Is there a function or combination of them that will allow me to achieve this?

regards
Peter