Since frequency anaylsis doesn't help with this code, it is likely a polygraphic substitution. Depending on what you are learning in your applied math class, some type of mathematical algorithm is applied to a group of letters to generate the cipher text. If you are studying linear algebra, then it is likely that letters are grouped into digraphs, and then multiplied by a 2x2 matrix key. The letters that are generated each represent two letters in the original text. You would need to find the matrix inverse to decode this, or your professor may have supplied the matrix key. The blocks of 5 letters are just the common way of grouping the digraph substitutions.