For subtraction of whole numbers within 1,000, the learner decomposes the numbers into hundreds, tens, and ones, finds the corresponding place-value differences, and combines those partial results to determine the total difference. The reasoning includes regrouping when a place-value part of the minuend is too small, while maintaining equivalence between the decomposed and original quantities; more advanced algorithms, larger numbers, and generalized negative-number methods are not included.
To use partial differences, break each number into hundreds, tens, and ones. Then subtract each place-value part and combine the answers.
Example:
First decompose the numbers:
The ones part, , is too small to subtract . Regroup one ten as ones:
Now the tens part, , is too small to subtract . Regroup one hundred as tens:
The amount is still ; it is just written in a different way.
Now find the partial differences:
Combine the partial differences:
Therefore,
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