I hate learning arithmetical tricks that I should have been taught in
school and wasn't. Like, these tricks aren't hard, and they're kind of
obvious once you think about them, but unless you deconstruct how
arithmetic works you may not realize they're even there. Stuff like the
below should be taught in schools.
I learned that to take a percentage of something, I just have to do the
multiplication. 16% of 410 mean I need to multiply 410 by 0.16. And that
probably will require paper and pencil or a calculator if I want to get it
right, because I can't do 410 x 0.16 that easily in my head.
Except that I can. I saw a video that laid out some hard truths about
percentages that I probably would have thought of if I'd ever thought about
it, but didn't, and so should have been taught explicitly.
Percentages are additive.
And yes they are, but unless you're explicitly taught that, you may not
realize it.
You can look at 16% of 410 as requiring you to multiply 410 by 0.16, which
I can't easily do in my head. That's the technique I learned in school.
OR you can look at it as taking 10% of 410 (easily calculable in my head as
41), then taking half of that (i.e., 5%, in this case 20.5, also easily
calculable in my head) and then taking 1% of 410 (also easily calculable in
my head as 4.1) and adding them together.
41 10%
20.5 5%
4.1 1%
----- -----
65.6 16%
And that's pretty easy to do in my head.
Why is this not taught in school? I get it's obvious if you are the sort
that deconstructs math, but most people don't do that. They just work the
techniques they learned in school. And this isn't one of those
techniques, or at least wasn't when I went to school. But it seems like it
would be *quite *useful to have known. It makes calculating 51% of things
a heck of a lot easier than it is using the standard "multiply it by 0.51"
method - calculate 50% (easy), calculate 1% (easy), and add.
Duh.
Scott
