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Anything to speed up or simplify calculations.

A simple example might be to get a multiple of $19$, for instance, $38 \cdot 19 = 38 \cdot 20 - 38$.


(This is hard to tag with so few tags in play!)

mental-calculations tips tricks shortcut cheats time-saver

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    I have started a meta thread, http://meta.math.stackexchange.com/questions/358/are-calculation-questions-acceptable2010-07-29
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    Please make this community wiki2010-07-29
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    the [New Math](http://www.youtube.com/watch?v=SXx2VVSWDMo) worked pretty well for me.2010-07-30

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