Bell Curve

Posted on February 22, 2023


They’re doin’ standard deviations in Math Literacy and I successfully found the sheets where I’d cut and paste a snip from an online page, with its copyright McGraw-Hill photographer because no, I don’t know how to draw a bell curve using Bezier curves 😛 When I went to the student I discovered they had a handout with … a bunch of them, because it was a practice worksheet to fill ’em in. Hypothesis/inference: teacher was inspired by my snips 🙂 (and aware of copyright!)

… and I was inspired to dive into GIMP and use the “select by color” tool and make a legit version. No, I couldn’t find a slanted “mean” symbol, and yea, I’m going to stick to the “not including the extremes” like the other images do because of the whole number sense stuff with using 50% as half. Yes, it’s public domain.

Yes, I think I’d like to make some that are scaled, so that a standard deviation of 10 is in fact different from a standard deviation of 50 because I think this is another example of something that folks calculate to death — yes, our folks have to do it the hard way a few times — as a Ritual Of Complicated Calculations. There are word problems that “this set of data has mean of THIS and STD DEV of THAT, and this other set has a close mean, but a bigger standard deviation, and they’re asked: True or False, more students did better (group w/ higher mean). Okay, my first problem is that the “correct” answer is false — when … WE DO NOT KNOW. Students learn to memorize “oh, the ones that say something about being close to average or spread out more or less? They’re all true.” … because they are. None of them make you *check* to see if the spread out one has higher standard deviation.

OOPS that image has a nasty little typo (+1 SD where it should be -2) and … I made another one, but did I get distracted from sharing it? Seems so. WILL UPDATE SOON!!! … and I decided to put in the teeny part at the end.

I also understood the “don’t put the teeny part at the end in” better when helping folks in Stats 108. TO use the TI-84, you *need* to add 50% to what you put in, or subtract what you put in from 50% to get a lot of “cumulative area under the curve” answers. I agree, tho’, with NOt Going There in Math LIteracy because they *only* have examples that are exact standard deviations from the norm. Sigh, *YES* I want to make some icons to have visual references for that and the whole “oops, it’s a sample, you have to change the standard deviation.”

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