Cite the error number

courses are stored in a matrix M. It is required from you

[Rik]

It looks like you edit away most of your question (or Andrei took a wild guess). If that is the case, please undo your edit.

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Answer 1

[Andrei Bobrov]

M = randi([1,200],15,8);

S = flip(string(['A':'D','F']'),1)
[~,~,a] = histcounts(M,[-inf,60:10:90,inf]);
out = S(a);