I was a tutor in business school on behalf of the MBA program. Basically, there was a small group of students who were... not prepared with respect to math. We're talking really simple algebra, maybe the simplest of differentiation (e.g. maxima of a simple quadratic function).

One of them told me one day "I don't understand graphs." I tried but it's impossible at that point to make up for an apparent total lack of at least high school level arithmetic/math.