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## 5 out of 6 Books

At first, this is what I thought the student had done:

• First, the student drew six circles to represent “out of 6 books.”
• Then, they distributed, one-by-one, the 66 books into each of the 6 circles. (If they just put 11 in each, why tally them?)
• Then, the student searched for a way to represent the “5 out of” that are non-fiction.
• It follows that the remaining books are fiction. That makes six sixes, or 36 books.

But then Bridget and Julie came in with a fantastic, different interpretation. Their’s feels like an improvement on my first draft.

We then got to work trying to come up with some activities to address this work. Suppose that your class of 6th Graders try this problem, and a lot of your class has struggles that are similar to the work above. You’re planning tomorrow’s lesson. What activity would you begin class with?

This is what we came up with. Which of these activities do you think would be most helpful? Are there any changes you would make to any of them? Is there a combination and sequence of these activities that you think would work particularly well? (I took a shot at sequencing them below. Some details on activity structures are here.)

Categories

## Bedtime Math Mistakes

From Bedtime Math:

Big kids: The record distance for a thrown boomerang to travel is 1,401 feet.  If it traveled exactly 1,401 feet on the return trip too, how many feet did it travel in total?  Bonus: Meanwhile, the longest Frisbee throw is 1,333 feet – about a quarter of a mile! How much farther from the thrower did the boomerang travel than the Frisbee?

From the submitter, who sends in the thinking of two of his students:

(1) first student, having doubled the boomerang distance in the earlier question, now doubles the frisbee distance  and calculates (2801 – 2666) feet.
(2) Second student gets an 100 board and spends a short time calculating 100 – 33 = 67. Then thinks for a long time during which I’m sure he is going to say 67 + 1 = 68, but never quite does it. I stay silent until he announces: 667. No clue where the extra 600 came from. He wasn’t willing to write down or draw anything to explain his thinking.
Interesting!  I’m inclined to put the first student in the “extending the thinking you’d do in one model to a less familiar situation” category and the second student in the associational mistake (same link) category.
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## Comparing Ratios: What Feedback Would You Give?

What feedback would you give to this student? Some considerations…

• Would you ask a question or make a statement?
• What written feedback would be most helpful?
• If you were able to have a conversation with this student, how would you start it?
• What would the student’s job be once you handed the paper back to him/her?
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## Cross addition isn’t a thing

Presented without comment, and with thanks to Andrew.

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## Cross-multiplying or Cross-cancelling?

The submitter reports that this happened with several different students who went up to the board to solve proportions problems. This was the “Warm Up” exercise.

How would you react to these mistakes in class?

Thanks to Victoria for the submission!

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## Money

Let’s not even call this a mistake quite yet. What does this answer reveal about what the kid knows?

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## Proportions

What’s the mistake? Why this mistake in particular?

Thanks again to Louise Wilson for the submission.