one thing for which flash cards are especially useful is making associations for number properties. see my second post on
this thread for details (should be the third post overall).
you should also make flash cards for the following:
* powers of 2, up to 2^8 = 256
* perfect cubes, up to 10^3 = 1000
* perfect squares, up to 25^2 = 625
the way to use these flash cards, by the way, is NOT to perform computations. in other words, if you have the card with "15^2" on one side and "225" on the other side in your hand, you should NOT look at the 15^2 side and say 225. that's a cool thing to know, but it's nothing you couldn't figure out with 5 seconds of computation. instead, the true value of the cards lies in using them the
other way: you should be able to look at 225 and say "oh, that's 15 squared".
THAT is the key. if you ever see a problem containing a 225 to be factored, you'll be able to factor it instantly, and you'll also know that any problem containing a 225 is likely to involve square rooting at some point.
by the way, if you have any family members between the ages of, say, 6 and 10, they will absolutely LOVE quizzing you on these flash cards.
awesome.
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as far as everything else that you can do with flash cards, here's my favorite rule:
if you discover an association between anything and anything else, put it on a flash card.
i am being serious.
good stuff.