This video is the last of three in which I describe common mental subtraction methods. The subtraction methods that we use on paper are, generally, too cumbersome for mental calculation. Also, we rarely subtract large numbers mentally ... so we use different techniques in this case ... ones that don't require remembering lots of detail!
In this case we actually find two differences and add them! By calculating how far one numnber is below, and the other number is above, some convenient reference number ... we then simply have to add those two differences.
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RATIONALE FOR THIS SERIES
Some of you have expressed quite some interest in different subtraction methods/algorithms. This resulted from my posting two lengthy videos in which I explained WHY different algorithms worked.
It became apparent, however, that I needed to create a series of much shorter videos in order to DEMONSTRATE these methods (and more) without the lengthy explanations in those first two videos.
