In-Class/On-line Group Inquiry/Discussion

Subtraction Errors

The following arithmetic questions show systematic subtraction error responses for five different children. There are three sample errors for each child, so each question in a set of three responses contains the same error. What is each student doing/thinking?

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Sample Response What's the student doing? What could you suggest to remediate this problem?

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37    43    85

-4      -1     -3

----   ----    -----

23    32    72

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32    50    24

-6      -8     -5

----   ----    ----

34    58    21

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53     72     45

-14    -56   -19

----      ----    ----

49      26     36

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The following arithmetic questions show systematic addition error responses for five different children. There are three sample errors for each child, so each question in a set of three questions contains the same error. What is each student doing/thinking?

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Sample Responses!                     What's the student doing?

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76    205      754

+17   +86       +28

-----     -----       -----

25       21         26

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519    345     483

+82    +76     +57

-----     -----     -----

511    511     711

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46     21     15

+3     +8     +2

-----   -----    -----

43     13     13

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46     21     15

+3     +8     +2

----     ----    ----

79    109    37

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48     79     26

+3     +9     +7

----     ----    ----

411  718   213

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