Sunday, August 5, 2012

Mental Math with Singapore 2B

I may have Willow start doing all her math in her head.

For a few weeks now, Willow and I have been working on adding one- and two-digit numbers using carrying. We visualized the process by setting up the equations with Base 10 blocks--

--then trading up and physically carrying the ten bars over to the next place before adding everything together, and finally moving into the conventional method of carrying while working arithmetic problems on paper.

 There was a lot of grumping, a lot of Base 10 block pattern building--

--and a lot more grumping, and the concept just didn't catch on. I'm pretty sure that the concept didn't catch on not because the kid didn't understand the concept, but rather because she was too busy grumping and pattern building to put the concept into her brain, but nevertheless, that's a lot of grumping and a lot of repetition just to learn (or NOT learn) carrying.

So we're just not going to learn that--not exactly, at least--right now.

In related news, last week my local indie teaching supplies store, which is normally too expensive for me to shop in, had their mid-summer sale, bringing their prices down to slightly more typical levels, and so I came home with the following:

  • one postage stamp collector's album for Willow
  • one book of world map post-its
  • one book of hundred grid post-its
  • one book of multiplication table post-its
  • a set of coin rubber stamps
  • the practice books for Singapore 1B and Singapore 2b
I avoid math curriculums because I have no problem teaching elementary math, but I do like the idea of having a logical order to work with, and I do like some of the mathematical concepts that Singapore math, in particular, teaches, so the reasoning behind purchasing just the practice books is that I can pretty easily figure out the concept that's being practiced, teach it on my own, and reinforce it with the books.

Singapore 2B has a lot of review in it for Willow, but I'm not opposed to drill and repetition, and there are a few key concepts in it that she hasn't explored yet, so that's why we settled there for her. Singapore 1B looks like a good fit for Sydney overall, so yay there for her.

My point with this digression is that, right there in the Singapore 2B practice book, front and center just before a money review and some new exploration of fractions, is a series of mental math practice problems that involve a different method of solving one- and two-digit addition problems, mentally, WITHOUT carrying. Here's what it looks like:


First, she's rounding the one-digit number to the nearest ten, and finding the difference, which is an easy subtraction problem. She's going to hold that number in her head. Second, she's adding the ten to the two-digit number, using skip-counting. Third, she's subtracting the difference from that new number, and it's another easy subtraction problem to the answer!

Now, do not even get me started on whether or not this method takes more steps than simply carrying the ten (it does), because for the little miss, that's not the point. The point for the little miss is, apparently, the fact that the steps are broken down into simple problems that she can do in her head. While the connection to the concept of what you're physically doing with the numbers isn't as clear, to me, as it is with carrying on paper, especially as visualized using Base 10 blocks, it IS still connected to the concept, just in a different way that seems to appeal more to the miss.

So this method, combined with simple "counting on" when the units to be added will add up to less than ten, gives Willow all the tools that she needs to mentally add one- and two-digit numbers to each other, abilities that we've been practicing with a homemade deck of laminated number cards:


And thus we can put aside that dreadful carrying altogether, to be brought back up at some point in the near future, preferably after the little miss has forgotten her grumps about it!

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