a quick math challenge

[aurelio]

(12-28-2013 10:06 PM)Les_Koller Wrote:  I teach 9th grade Alg 1, and am happy to report approx 80% of my students rember the 2, 3, and 5 rules. Cannot figure out why they can't remember the by 6 rule!

For me was simple to remember the 3, 2 and 6, a bit more difficult the divisibility by 7, I'd right now to check again on wiki the last one.
Rules by mind are made to be forgotten if non applied, I don't mean daily, but often........