Tristan! This stuff is fabulous!!! Thanks!!!
My oldest is studying algebra, she does not particularly like math, so whatever she learns she often tosses aside after she finishes a unit. She has been having trouble deciding whether she can simplify a fraction when the numerator or denominator is a large number, so these divisibilty rules will be a big help to her.
Also, I see that a rule for the number 7 is only contained in one of the charts. Is that simply because it is so complicated? It does seem a little too complicated to remember very easily.