Or just a parody of one?
I don’t follow it, but it sorta’ looks like it could be an example of “subtraction equals negative addition”- the sort New Math-y thing some attempts were made to teach.
Well, first of all 12-3=15 is wrong. Should be 12+3.
And I am not familiar with the new math, and I guess that is one way to solve that problem but man, it’s a convoluted one.
How old are you two? Because if you’re under about 50, then you are familiar with New Math, because it’s what you were taught in school.
Above 50.
Interestingly, Googling New Math gives an exact explanation of it:
http://www.patheos.com/blogs/friendlyatheist/2014/03/07/about-that-common-core-math-problem-making-the-rounds-on-facebook/
And yes, it should be plus 3, not minus 3. It looks like whoever made this image didn’t realize that the vertical line on the plus sign was covered up by the box.
If we believe Kline (reference given in Wikipedia), then New Math includes modular arithmetic, algebraic inequalities, bases other than 10, matrices, symbolic logic, Boolean algebra, and abstract algebra, none of which have anything to do with the blackboard problem. It therefore seems like a second-rate parody.
ETA or, if not a parody, nothing to do with New Math.
Shrug. Perfectly valid way of solving a problem.
Ever do 92 - 5, and do it as 92 + 5 - 10? 97 -10. 87.
There’s absolutely nothing mysterious about utilizing associative properties of operations.
And it actually makes sense. I’d go for it.
There are lots of valid ways to solve a problem. Not sure how that way makes it any easier.
(btw if you hate subtraction, just complement the number: 32-12 becomes 32+88, 92-5 becomes 92+95, is my advice)
The graphic is telling you how it works.
Instead of looking at the problem as trying to subtract 12 from 32 - they look at it as counting up from 12 to 32.
How is that better?
That’s something the predates new math and is a lost art today: counting up change. The only difference is that arbitrary numbers are used instead of coins.
To count up, let’s say something was $1.27 and they gave you two dollar bills. No need to subtract the difference. You start at $1.27, grab three pennies (counting 28, 29, 30) and then two dimes (40, 50), and two quarters (or a fifty cent piece).
This was taught in schools until the 70s, when cash registers could calculate change. So not only is it sensible, it’s not even new.
For you, it might not be. The point is to show lots of different ways to solve problems so that kids can find one that works for them.
Most of the criticisms of “Common Core” (what I suspect is meant by “New Math” here, and still a misnomer at that) boil down to: “The teachers are showing kids lots of ways to do things, and some of them aren’t the way I was taught, therefore it’s wrong!”
I would solve the problem as
32-2 =30
12-2 = 10
30-10= 20
But I do math weird.
That may be. But they are not teaching kids to convert to binary or octal and then adding. Aren’t they ways to solve problems? Why this way? Just seems like a lot more work for little gain.
enalzi’s link debunks the notion this has anything to do with Common Core any more than it has to do with New Math. (Of course we have all seen the cashier hand back change that way, but that is not the point.)
Not only do good math teachers teach multiple methods to solve problems, and not only do some kids have an easier time with some methods than others, but sometimes different methods are easier for some problems than others. The new way of doing subtraction that most of us learned, with the borrowing and so on, happens to work very well for this problem, so it’s a poor choice for demonstrating the old counting-up method shown on the chalkboard there. But try it again for 32 - 15, and you’ll find that the old method shown on that chalkboard is a lot easier than the newfangled borrowing method.
The sample way takes 4 steps to calculate the subtraction. The “carry” way takes 3 steps. How is the sample way easier?
Because the steps themselves are easier.