COMMON CORE MATH MOMENT #5 Ive had several people comment that schools should still teach the basics before going into tricks like changing 530-270 into 560-300. For what its worth, I completely agree. That makes sense to me. I bet it makes sense to you too. I bet it makes sense to the teachers in Shanghai, Singapore, Taiwan, etc, too. And it probably makes sense to some common core math teachers in the US. It might even be a lot of math teachers in the US. But as todays video shows, its definitely not ALL math teachers in the US. Listen carefully to what the girl says at the 3:35 mark. They are not allowed to stack. (Yes, this is last Saturdays video again. I promise a new video tomorrow.) Just to be clear, lets review what the basics are. Well, the basics look like this. 530 -270 ------ 260 This is the stack that the girl in the video was talking about not being allowed to do in the video. Nevertheless, the problem I have with parents who want to go back to this is I wonder if they actually know why it works in the first place. It works because of place value. (Side note - dont get Paula started on place value unless youve got several hours. She will talk your ears off about how important it is.) The stack helps you to subtract 2 HUNDREDS from 5 HUNDREDS, and 7 TENS from 3 TENS, etc. the key is that you are subtracting LIKE things. Hundreds from hundreds and tens from tens. They operate like units. You wouldnt subtract tens from hundreds, or vice-versa, no more than you would subtract 1 MILE from 3 GALLONS. And the answer is not 2 because the fact that 2 is positive implies that 3 gallons must be greater than 1 mile. But I could instead write 1 mile as 5280 feet and now weve got 3 gallons minus 5280 feet, which is negative, thus implying that 3 gallons is less than 5280 feet. But 5280 feet is just 1 mile. See the problem? (Another side note - I used to torment Erica and Rachel with questions like this! Fun times.) You can see in the video how the girl is sorta on the right track. She talks about how a cube represents thousands, a sheet represents hundreds, lines represent tens, and dots represent ones. It does have its merits. But she is not allowed to stack. Hmmmmm. And the guy at the end claiming that the traditional system is tried and true? Well, recall that we are 27th out of 34 countries in math. And there are plenty of other examples out there about drawing sheets, cubes, lines, circles, you name it. Oh well. Perhaps the worst thing is that the whole subject has become politicized. More tomorrow, and a new/different video. Promise.
Posted on: Sat, 16 Aug 2014 18:57:29 +0000
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