Ideally, I am looking for an online resource. But a book or any other would help already.
Background: I am a senior teaching assistant in the field of business and statistics. Most of my students have not had formal training in mathematics, and neither have I. I notice many of our students have difficulty following the professor's lectures for the trivial reason that they do not know mathematical notation (the professor does have a math background). In my experience as a schoolkid and student, no-one has ever explained how to read an equation. The only reason I know, is that I have cobbled it together from what my professors have said while pointing to their equations, which they always acted we knew how to read already.
I have made some effort to look for such a resource with my search engine, but have not found anything approaching what I mean.
Caveat: I appreciate that there are many subfields of mathematics, and that they use vastly different notations. A general resource would interest me most (and be most useful to future readers of this question), but in my case I am specifically in need of the notations needed in statistical calculations, so: sum, estimate, average, indexing, etc.