• Albbi@lemmy.ca
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      1 month ago

      I do, because 9 plus anything is just a 1 in front of the other digit minus 1.

      Weirdly enough, I just thought about using the methods here for the first time in my life earlier today. Weird.

    • don@lemm.ee
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      1 month ago

      Yep, there are many ways that people (some of whom may or may not be of earthly origin) have developed to perform various degrees of math all in their heads.