I prefer to write longer blog posts than this, but it was slightly too long for a Facebook status. So it goes here instead.
So I've been seeing posts (okay, two, but that's still plural) about the stupidity of the new Common Core methods for math education (example here, if you haven't seen them). Haven't said much, because I didn't really have any evidence to cite either way - both methods shown work, but I also couldn't come up with an argument for why the latter should be preferred.
Then what happens? I needed to figure out 3550 - 2680, didn't feel like pulling out a piece of paper or the computer's calculator, and caught myself doing the following in my head:
2680+20 = 2700
2700+800 = 3500
*800+20 = 820
3500+50 = 3550
*820+50 = 870
And then I realize I've been using this same method for mental math for years, because I find it easier to remember two running totals than trying to mentally run the traditional algorithm. Maybe there's something to the new method after all...
(More comprehensive response here... and from two months ago. Why are we still talking about this "problem"?)