When You Multiply by 10, Just Add a Zero? Horrors!?!



Monday, October 1st, 2018
Have you ever asked students to solve 12.6 x 10, and they respond that the answer is 12.60? I have, many times. Students who do this apply a pattern that works when they multiply whole numbers by 10—they tack on a zero to the end of the number they’re multiplying. But then they apply the same pattern when working with decimals. What can we do?
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When Should and Shouldn’t We Give Answers?



Sunday, February 5th, 2017
Over a year ago, I blogged about The 1–10 Card Investigation. I didn't provide a solution to the problem and no one who commented asked for one. But a newly posted comment requested the solution. That pushed me into a conversation with myself about how I should respond, and about giving answers in general.
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An Oldie Revisited: The Border Problem



Tuesday, April 19th, 2016
Here's one of my favorite oldies. (No, not the photo—the border problem.) I was so pleased to see this math investigation included in Jo Boaler’s latest paper. This blog post presents a detailed lesson plan for using the border problem with students and also includes a five-minute video clip to give you a sense of how the instruction went with one class.

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