# Guided Tour

Stella problems have an index number and a title, like this: **2860.51 – Robot Stones**.

The 2000 part of the number tells us that it’s an algebra problem. The 860 is the subcategory within algebra (see below). And the two-place decimal completes the problem’s unique index number. This problem seems to be something about robots, and something about stones. Hmm.

The Stella problem library is like a library of books. The Stella Decimal System is like the Dewey Decimal System. The Stella Decimal System (SDS) has ten over-arching categories, which you can see here. One of those categories is algebra, 2000. The number 860 tells us that the problem involves arithmetic sequences. There are three hundred and fifty of these subcategories, spread amongst the ten over-arching categories. The list of subcategories is here (listed alphabetically) and here (in numerical order).

On the top of the sidebar to the left is a list of problem sets, which we think you might find handy for use with your students. There are eighteen such problem sets. Why eighteen problem sets? The idea is to give you enough to get you through the school year if you use one every two weeks or so. We have tried to arrange the content of these problem sets to coordinate, more or less, with the material being taught as the year goes along.

Within each problem set are five subsets of 6 to 8 problems, that you can use for five different courses: Pre-Algebra, Algebra I, Geometry, Algebra II/Trig, and Pre-Calculus (or, "advanced" math). You can also use the links in the sidebar to quickly filter problems in these categories.

Each of these small sets of problems starts with an “easy” visual problem – a grabber, if you will. Then comes something involving numbers, then algebra, on up to a rough guess about what the particular course might be studying at that point. We did our best about this. For instance, the geometry problems in set 9 (halfway through the year) end with a problem that we think would be a review problem, and with a problem related, maybe, to what’s currently being studied. As I said, these are a rough guess.

The material in the “Browsing & Downloading” section will show you how to make these subsets.

By the way, **there are no problems that appear in more than one problem set**. You could give your students Stellas for five years, using the problem sets, and they would never see the same problem twice! (But, thus, if you edit a problem set and stick in something else, you might find it turning up in another set later. Be ye warned.)

Each problem comes with three tags, indicating the set that it’s in, the course that it’s in, and what kind of a problem it is (among the 13 overall topics).

The Introductory Problems are also discussed in the "Browsing & Downloading" section. These problems get at the heart of the heuristics that the Stella Library is designed to target.

Finally, about set 99. These are problems that aren't in any of the 18 official problem sets. This is where we add more problems that we find. If you send us nifty problems of your own to add to the library (hint, hint), this is where they'll go.