I can provide a file with a sound sample and the cepstral coefficients, so that they can check their answer. Unfortunately, I haven't been able to find a really good intuitive description of the meaning of MFCCs that doesn't rely on heavy-duty signal processing theory. So yes, it's kind of a black box at this point. The reason we are doing this at all is because originally, the discussion of cepstral coefficients was part of the Voice Recognition lab, but it seemed rather out of place there, so we moved it here. I wish there were an easy and cool application of cepstral coefficients that the students could do right away, but there isn't (as far as I could tell).