So for this What Do You Notice? poster, I decided to tie in rectangular arrays with prime and composite numbers.  That said, whatever math-y thing students notice is totally acceptable.  For example, one student noticed that the “buildings” had square windows.  Great.  That’s a little bit of geometry.  Another student noticed that each set of colored rectangles included the same number of squares.  Again, great, as that required some counting and comparison.  Just like the student who noticed that there are more yellow squares than any other color square.

As far as the prime and composite numbers…yep, we got that covered, too!  Here’s how David described it on his post-it, “The first 3 are composite, the last 2 are prime.  There are different arrays for each number.”  And he’s right.  The composite numbers have more than one rectangular array while the prime numbers only have one array.

But here’s an observation I totally didn’t notice.  “The columns go one higher, one lower.”  And, indeed, they do!