CaféAuLait
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Find the person or persons responsible for such math bullshit and lock them up forever.
It is a math trick that can work for quickly approximating answers, but it doesn't really provide usefulness in a real world context as no job I know of is content with approximations.
A similar math trick is in calculating multiples of 9.
9 * X = (X-1)*10 + ( 9-X+1), for example 7*9 = [(7-1)*10]+(9-7+1) = 63.
While the trick works it is far faster to just memorize 9*7=63.
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