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Why the Standard Algorithm for Multiplying Whole Numbers Works from Mathematics for Elementary Teachers by Sybilla Beckmann page 189

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Why the Standard Algorithm for Addition and Subtraction in Base Ten Work from Mathematics for Elementary Teachers by Sybilla Beckmann page 119

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The Counting Numbers
from Mathematics for Elementary Teachers by Sybilla Beckmann page 11

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This is in peergrade.

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This is in peergrade.