# Does this video depict an accurate example of a Common Core math problem?

The following article has been circulating which includes a video that demonstrations a Common Core math problem: "This Common Core Math Problem Is So Absurdly Difficult It Stumps College Students and Teachers" via Independent Journal Review. In the video, the following steps are taken to solve the math problem "32 - 12 = ?" (summary from Slashdot):

To solve 32 - 12 = ? you do the following:

12 + 3 = 15

15 + 5 = 20

20 + 10 = 30

30 + 2 = 32

Then 3 + 5 = 8, 8 + 10 = 18, 18 + 2 = 20. Therefore 32 - 12 = 20.

Is this an accurate depiction of how math is being taught or is it being grossly exaggerated and is an instruction technique of more limited use like base ten blocks.

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Am I missing something? Where do the numbers come from in those 4 sums? – Jamiec May 22 '14 at 14:54
This is a valid technique for subtraction. I believe cashiers do this all the time, even though they just collect the coins as they go instead of summing their steps afterwards. – Jens May 22 '14 at 15:00
@Jens - What is the technique? How does one go from the problem (32 - 12) to the 4 sums following? – Jamiec May 22 '14 at 15:01
@Jamiec: They are imagining something like counting back change. To figure out the difference I start from 12 and add 3 to get 15, add 5 to get 20, 10 to get 30 and add 2 to get 32 (where we started). The sum of the bits we added is 3+5+10+2=20 (the difference). This is not how I would have written this, but it is a working algorithm for subtraction. Many of these "Here's a bad common core question" posts seem to involve working algorithms that are unlike the "usual" system. I conclude that the idea is to offer a lot of methods and hope each student learns at least one. – dmckee May 22 '14 at 15:36
Aside from the obvious extra steps, it seems a little tautological to me anyway -- at each step, you kind of implicitly have to do subtraction anyway (when the sum gets to 30, how do you know it's 2 you have to add to it to get 32? You could say you 'count up' to 32, but you also kind of had to know earlier then that it was okay to add 10 to 20). – YungHummmma May 22 '14 at 16:36