| Indeed, the sum is a polygon whose vertices are obtained as the sums of vertices of the addends. |
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| The width of the sum in any direction equals the sum of widths of the addends in that direction. |
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| The children then call out the addends — make that the numbers — in unison. |
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| Describe strategies for solving problems involving missing addends. |
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| Students' answers to some of the problems show that they were capable of finding missing addends or subtrahends. |
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