Math Warm-Ups February 11-14, 2013

Another 4-day week for us, but only a 3-day warm-up week because of some very messy cubbies that needed to be attended to on Tuesday morning.  Happy calculating!


IMG157Can you catch the mistake I made in this warm-up question?  I didn’t catch it until we started discussing how to do it and figured out that you can’t round a decimal to the hundredths place if it’s already a hundredth!  So we changed it to tenths.  Oops.  HATE it when that happens, but LOVE that it continues to teach my kiddos I’m not perfect.  Teachers don’t know everything and they do make mistakes.  And we know how to solve problems like that when they happen.  So I guess in some ways this was a double-whammy warm-up: two lessons in one!  Only wish I’d planned it that way….:)


Oh, yeah, we were cubby cleaning.  There was too much mess to take a picture, so nothing to share here.


IMG158We had been working on place value and rounding with decimals for about a week and were ready to move on to adding and subtracting, which I was figuring would be pretty straightforward, and so relatively easy.  The way this one was worded, though, caught a couple of kiddos because they wouldn’t remember what “sum” and “difference” meant–definitions we reviewed as we went over the problems.

That second problem sparked another one, too, which was a goodie:

IMG159What do you do when you have a whole number and you subtract a decimal?  There isn’t a decimal to line up.  Or is there??


IMG160There’s a joke in this warm-up (that’s probably only funny to me and my class).  See, we were noticing on Wednesday that many of the word problems we have in our math book involve running (Sally ran .89 of a mile on Monday, 2.3 miles on Tuesday and .5 miles on Wednesday, etc.).  In our groups we’d been talking about how guilty those references made me feel since I’ve been REALLY lazy about my running the last few months.  So Thursday I made the problem all about my running.  But since I can’t lie about what’s really happening, I made sure to say that we should pretend that I ran all those miles last week.

But aside from making us all laugh at my funny joke, there was another reason I wrote the problem the way I did.  We are going to be moving into multiplication of decimals next week and I wanted to see what they could do with that.  The problem could easily be answered without multiplying, too, for those that weren’t ready yet–and some just used repeated addition to get the answer–but some did try multiplication as a strategy.  Many of those figured out just what to do with the decimal point, and did so in a logical way–which I loved!  Rather than spouting off the rule about having the same number of decimal places in the answer as in the problem, they used what they know about the problem.  They got to the number 2282, and when thinking about what the final answer should be, thought “Well it can’t be 2.282 because that’s not even as far as she ran in one day.  It can’t be 228.2 because number is WAY too big.  22.82 makes sense because 3 miles times 7 days is 21 miles and the answer has to be a little bigger than that.”  THAT is the kind of thinking I look for and was so excited to see as I threw them this new concept.  It makes me excited to hear and see more as we dig in deeper this upcoming week!

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