Note the “e.g.,” which means, “exempli gratia,” which means, “for example.” This is an example of how to interpret products of whole numbers, not a directive for how to always interpret products of whole numbers.
Indeed, there’s a closely related standard:
It looks like this kid used the commutative property of multiplication as a strategy to multiply.
If someone–a parent, a teacher, an administrator, a textbook company–isn’t reading carefully, they might conclude that the common core standard wants kids specifically to interpret 3x5 as three groups of five. But that’s not at all what it says, and the entire thrust of common core mathematics is to move kids to a much more abstract, fluid way of understanding math. What validity there is to complaints against common core math, at least at younger grades, consists of criticism about the inappropriately early move to abstract reasoning among a population that’s generally in the concrete operational stage, a move that might deny kids the intuitive grasp of numbers that builds the foundation for later work.
But there’s no validity at all to blaming common core for this particular error.
My thoughts on how to justify the grading, and what I assume is being gotten at:
(As was previously mentioned) 3 bags with 5 pieces of candy each is a different collection of objects than 5 bags with 3. Three hands, each with a whole hand full of fingers is a different kind of collection than 5 collections of 3 fingers. But, because multiplication is commutative, 3x5 = 5x3. This later gets contrasted to division, subtraction, which aren’t commutative.
The important thing for kids to know, though, is that in whole-number addition, subtraction, multiplication, and division, in which the equation has three numbers, you can always switch the places of the two smaller numbers and get the same result.
So:
2+5=7
5+2=7
7-2=5
7-5=2
2x5=10
5x2=10
10/2=5
10/5=2
They don’t need to know that in multiplication and addition this is called commutativity; they just need to know that you can do this, and that sometimes fiddling with the position of numbers makes solving the problem easier.
And they need to know that when you’re solving a word problem, it’s completely legit to fiddle in this way. It’s a lot easier for a lot of kids to solve 200-2=___ than it is to solve 200-=2, for example, and depending on your method, solving 123+13= is much easier than solving 13+123=___.
They should learn a similar lesson about the relationships between multiplication and division, and between addition and subtraction. If you go through life solving 374-138=___ by switching it around to 138+=374, that’s cool–and if you want to remember 72/9= is 9 x ___=72, that’s lovely.
It’s all about knowing how math works so that you can be flexible in your problem-solving strategies. Counting answers like this wrong is going to lead to infelxible, borderline superstitious thinking about how math works, and that’s entirely the wrong approach, IMO.
[I was always amused at what a big laugh he gets for saying “the important thing is to understand what you’re doing rather than to get the right answer”. At the level of college-level physics, we so routinely give nearly full credit for a generally correct solution even if the actual numerical answer is orders-of-magnitude off … and nearly no credit for guessing and getting it much closer … that it hard for me to even imagine doing otherwise.]
The kind of thing I had in mind was trying to use the “you can always switch the places of the two smaller numbers and get the same result” rule when doing things like 2 divided by 10, or 3 minus 5.
There used to be a time when a teacher could be an idiot and make a mistake on a child’s paper without having it broadcast over the entire internet. It’s actually pretty depressing to see one teacher’s fuck-up somehow get transformed into evidence of systemic corruption and an Obama-led conspiracy to destroy America’s youth.
Huh. I see what you mean. In that case, once non-whole numbers are introduced, the rule can be referenced and modified: The divisor and quotient may be switched, just as the subtrahend and difference may be switched. Point out that with whole numbers in subtraction and division, the dividend and the minuend are always the largest numbers.
But you’re right, I should probably be more careful in how I teach this rule, pointing toward the position of the numbers rather than characterizing them by their relative values. Thank you!
The solutions are different, and the first pair of numbers are whole while the second pair both possess a non-zero digit to the right of the decimal point.
If one is confused by the decimal (as I incorrectly took the initial comment to be about), one can just remove it temporarily, do the math of the “easier” first problem, them reinset the decimal afterwards for the right answer. The math process is the same, even if there’s a perceived increase in difficulty because of the decimal place.
This works only in the special case where all numbers in operation possess the same number of non-zero decimal digits. It also evades the whole point of learning to calculate using decimals.
You can add in place holders as necessary. To wit: 137.6 - 124.33 can become 13760-12433, with the two decimal places added back in afterwards. It’s the method actually preferred when doing long division involving decimals. i.e. divide 156 by 3.4. You change the problem to 1560 divided by 34 to make it “easier”. Note that it’s not impossible to do it with the decimal, but that it becomes cumbersome. My point however is that the decimal places are just another metaphor used in math that can be used or discarded as desired, and that understanding how the numbers operate in relation to one another is what’s important. Seeing beyond the metaphors is what creates real understanding in math. I wouldn’t particularly recommend this method to everyone as it’s more of a stepping stone, but then again, there’s scant few methods that I would recommend to everyone.
Well, to be fair parts of the RW were on board for state standards, testing and NCLB, etc for a long time. I believe the thought was that they could use poor results from certain public schools as a club against them (to help implement charters and vouchers). When that didn’t really work out, they seized on the standards (that they pushed to get implemented!) as the next whipping boy (in order to get charters and vouchers implemented).
If public schools dropped all of the current RW bogeymen tomorrow (common core, standardized testing, etc.) they would turn around and lambast public ed for the lack of accountability the next day.
Yup! As I said, you get the same result: you’ve successfully solved the equation!
(I wrote loosely there, but I think what “result” meant was pretty clear: I clearly didn’t mean you’d get the same number on the right side of the equation.)
In the sense that both equations express the same (true) relationship among the numbers 7, 5, and 2.
The word “result” can refer to the numerical value you get at the end of a calculation, but that’s not the only way the word is used, and LHoD already clarified that he wasn’t using the word to mean “the number on the right side of the equation.” In higher math especially, the word “result” is also used to refer to a fact, like the equation “seven minus five is equal to two” as a whole, rather than to the number 2. That’s how the word is used in, for example, Wikipedia’s "list of mathematical jargon: