35 – distance problems

In our Glencoe algebra textbook, D=rt problems are lumped in the same section as Mixture problems. I get it. And I don’t.

Maybe I’m kidding myself or in denial, but this year I’ve been saying this phrase a lot in class: Do what makes sense.

I’m tired of using tricks, mnemonics, pre-made grids to help kids learn. Like this question in the textbook. No!! I don’t want my kids to “copy and complete” anything!

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So as we look at each D=rt problem, I’m asking the kids:

  1. draw a picture
  2. what do you notice?
  3. what else do you know just by looking at known information and the picture?
  4. what seems like a natural question to ask about this scenario?
  5. set up D=rt for both items that are moving
  6. which of the variables — D, r, or t — stays the same?
  7. we don’t know the distance traveled by each of the cars, but we do know total distance, so how do we express that?
  8. when we multiply these two quantities, what do we get? what does the answer represent? what’s the unit?

I had them whiteboard these problems. I stole the cartoon from Chris Hunter’s post (most awesome post, by the way 🙂 — but I had to do some caption edits.

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I don’t know. I’ll see how they do in the next few days, but I really want the kids to make sense of problems from scratch, without any help from anything or anyone — just start something that makes sense!

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