The Official WTF Thread

[wart57]

No wonder I have trouble helping my girls with their homework.

Why is this WTF? Figuring from the nearest 10 is a great way to do computations and if you can do the problem this way, it's a decent indicator that you actually know what you are doing. The "old" way, suggested by the anchor, of just memorizing a bunch of math facts is not a good approach to learning.

But kids are not allowed to do problems the old way without getting points taken off. I have seen it in my kids grades, and on their papers. It is being taught as the only way to come up with the answer, not another way.

[Arthur Dent]

I agree with not giving full credit for just memorizing answers. If you can only give memorized answers without knowing the actual logic of what adding actually is, you haven't actually learned addition. Memorized addition facts are ultimately of little use. Understanding what it is and how to use it is, and should be, the real goal.

[wart57]

Is it easier for the kid to break up a 6 in to a 5 and a 1 and add the 1 to a 9 and then add 5 to a 10 than to remember that 9 plus 6 = 15?

That seems like a whole lot of work to come up with a simple answer.

That is why it is WTF to me.

I do see the logic behind it when dealing with much larger numbers though, that is the way I always do quick math in my head on large numbers, but people always look at me like I am nuts when I explain how I got an answer so quickly.

If we are teaching everything on base 10 now, why have we not switched completely over to the decimal system, things would be a lot easier then.

I am a [expletive] idiot, and if schools are teaching kids to do things the way my stupid brain works, we are all in a [expletive] load of trouble.

[Arthur Dent]

The point is not that it is an easier way to do that one problem or single digit addition in general. But if you know how addition actually works, you will be able to use these sorts of tricks. That pays dividends when working with larger numbers, but it is also important because knowing the logic means you have some hope of catching your own mistakes, knowing whether an answer is reasonable, being able to know when to use addition to solve real problems, etc. Memorizing the single digit addition facts gets you nowhere.

Edit:

I do see the logic behind it when dealing with much larger numbers though, that is the way I always do quick math in my head on large numbers, but people always look at me like I am nuts when I explain how I got an answer so quickly.

Math literacy is not especially high in the U.S. and this kind of thing is an indicator of that. Most people have been taught the memorization and fixed procedures approach to math. That can solve quiz problems, but it doesn't give you real math literacy, which requires a deeper understanding. Not being able to see understand the problem and see the multiple routes to a solution are a consequence of teaching match as plug and chug.

[pioneer98]

My kid had problems like 22783 x 7 written out sideways like that, and are expected to be able to multiply that in their head.

I mean, he ends up doing the math in his head (3 x 7, carry the 2, etc). I can do that if I write the numbers I'm carrying over. But my 5th grader can do all that in his head. I had to use a calculator to double check I did some of them right.

[Vidor]

My daughter's in 2nd grade and it's all about Common Core, dividing numbers into blocks--seriously, a larger block to represent 10 and smaller blocks for the 1's.

Makes me wonder how equipped children are to do math when they can't draw a picture.

[Arthur Dent]

My kid had problems like 22783 x 7 written out sideways like that, and are expected to be able to multiply that in their head.

I mean, he ends up doing the math in his head (3 x 7, carry the 2, etc). I can do that if I write the numbers I'm carrying over. But my 5th grader can do all that in his head. I had to use a calculator to double check I did some of them right.

I don't know that it's all that important to be able to do that problem exactly in your head. What would be useful, for example, would be to realize that the answer will be between 140,000 and 175,000 (20,000 x 7 & 25,000 x 7). In fact, it's very close to half way between those, or 157,500. If you can do that in your head, then when the calculator says the answer is actually 159,481, you know that makes sense.

[wart57]

My kid had problems like 22783 x 7 written out sideways like that, and are expected to be able to multiply that in their head.

I mean, he ends up doing the math in his head (3 x 7, carry the 2, etc). I can do that if I write the numbers I'm carrying over. But my 5th grader can do all that in his head. I had to use a calculator to double check I did some of them right.

I don't know that it's all that important to be able to do that problem exactly in your head. What would be useful, for example, would be to realize that the answer will be between 140,000 and 175,000 (20,000 x 7 & 25,000 x 7). In fact, it's very close to half way between those, or 157,500. If you can do that in your head, then when the calculator says the answer is actually 159,481, you know that makes sense.

Close enough for government work.
So, to get 9+6 you need to know 6-1=5, 9+1=10 and 10+5=15. Instead of memorizing 9+6=15. Makes perfect sense.

[ghostrunner]

The biggest obstacle is trying to help kids with homework. By and large, the kids seem to get it. I looked up online how to do it in one case, and found that it was the way I actually used to do math in my head.

None of this is common core either. Common core is a standardized set of skill requirements. I.e., - be able to add fractions. How the kids get there is still often up to the school system, teacher, etc. From what I understand they often teach multiple ways, because kids learn and understand differently.

[ghostrunner]

So, to get 9+6 you need to know 6-1=5, 9+1=10 and 10+5=15. Instead of memorizing 9+6=15. Makes perfect sense.

Memorizing is a quick way to a result, which isn't the point. The point is to give kids a method to find other results.