Written algorithms for
subtraction
In the primary school children are normally taught a formal written computational procedure for subtraction. The most commonly taught procedure is the decomposition (also known as renaming) algorithm, and the other is the equal addition algorithm.
I will illustrate the use of each algorithm to find this difference:
Before applying any algorithm it is a always a good idea to first estimate the difference as a rough check on the answer obtained by using the algorithm. Rough estimates can be found in many different ways. For example, one way would be to approximate this subtraction as 70 take away 40, so that the answer is about 30.
Decomposition/Renaming Algorithm
Click here to see how decomposition is done:
Click here to read a written description of decomposition.
Click here to see other examples of decomposition:
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Click here to see a variation on the decomposition algorithm:
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Click here to see how the decomposition algorithm is done with MAB (MultiBase Arithmetic Blocks).
Equal Addition Algorithm
Click here to see the equal addition algorithm being used:
Click here to read a written description of equal addition.
Click here to see other examples of equal addition algorithm:
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Click here to see how the equal addition algorithm is done with MAB (MultiBase Arithmetic Blocks).