Why '5+5+5=15' is wrong under the Common Core

Business Insider ^ | October 25, 2015 | Jacob Shamsian

[grundle]

Here's a "repeated addition" Common Core problem that's taught in third grade in US schools:

Use the repeated-addition strategy to solve: 5x3

If you answer the question with "5+5+5=15,” you would be wrong.

The correct answer is "3+3+3+3+3.”

Mathematically, both are correct. But under Common Core, you're supposed to read "5x3" as "five groups of three." So "three groups of five" is wrong.

According to Common Core defenders, this method will be useful when students do more advanced math. This way of reading things, for instance, can be used when students learn matrices in multivariable calculus in high school.

But parents aren't happy about it.

[Paladin2]

5 x 3 = 3 x 5

It's not just a good idea, it's The Law.

[W.]

The 'teachers' seem to be trying to make their students stupider.

Glad I learned the old-school way!

[rigelkentaurus]

this is stupid - seeing 5x3 as five groups of three and not 3 groups of five has nothing to do with learning calculus. If you don’t understand they are the same, you have zero hope of learning calculus anyway.

[MUDDOG]

I fought the Core, and the Core won.

[Jeff Chandler]

This way of reading things, for instance, can be used when students learn matrices in multivariable calculus in high school.

Because so many American pupils take calculus in high school.

[FourPeas]

By the time one gets to multivariable calculus, the point is moot.

[timestax]

bump

[kjam22]

[Ingtar]

5 X 3 = 15 and should not need to be factored out if they were still memorizing their tables.

[oldbrowser]

It's not just a good idea, it's The Law.

Does common core do algebra?

[tet68]

Honestly, I used to think I received a poor education
in the 1950s, now I bless it.

[17th Miss Regt]

And calculus in high school is single variable, not multivariable. It is a rare high school student who knows what a partial derivative is, much less be able to use it intelligently.

The Communist Core swamis have lost touch with reality. They want students to be able to think abstractly but don't care to teach them prime factorization of numbers, how to do operations with fractions or even make them learn their addition and multiplication tables. Idiocy only academics could believe.

[Dr. Sivana]

I would like them to learn the Commutative Law of Multiplication before worrying about higher Calculus.

For the record, I took Calc 140s (mid level) in a college known to have a good program, and also known for NOT invoking grade inflation, and these matrices never came up. I also took Honors Calc in prep school, and they didn’t come up there, either. Admittedly, it was not my best subject.

[kjam22]

I got mine in the 60’s and 70’s. You gotta wonder what idiot decided memorizing multiplication tables wasn’t the way to learn multiplication.

[tet68]

memorizing their tables.

Come on, that would be HARD!
Some can’t do that so it’s only fair that
none can do that.

[17th Miss Regt]

It is not so much that common core does algebra as that common core does it in.

[GraceG]

(5 + 5)=10
(10 +5)=15

Screw you common core, there is no “correct way” in math.

It is like thinking about the “climate” common core is a orthodoxy that is put in place to control HOW you are SUPPOSED to THINK.

Not “TO THINK”

[gop4lyf]

I teach 4th grade Math. This year at our Open House night, I had to prove to several parents that we don’t use Common Core lessons or curriculum. I don’t blame them. From what I’ve seen, Common Core math does nothing but confuse kids. I just started teaching them long division last week, and I shudder at the thought of my kiddos trying to learn it using Common Core strategies. If I won’t subject my own kids to it, I sure as heck won’t to other children either.

[Svartalfiar]

Hmm.. Under the commutative law, 5x3 = 3x5. So it's kinda an extra step 'show your work', but it's not wrong. Does common core not teach commutative, transitive, associative properties, etc?

This way of reading things, for instance, can be used when students learn matrices in multivariable calculus in high school.

Huh? I went to a private school, and was one of the more advanced ones. Taking a combined algebra/Pre-Cal class junior year, we had the option to take AP Calculus, AB or BC. But normal-track students didn't touch calculus, much less do much if anything with matrices. And as far as I can remember, matrix multiplication is the only time when axb =/= bxa. And I don't even remember the different between cross product and dot products.