[Hugin]

I invented my own ways of doing arithmetic in as a kid. In their example, I knew that 293 was seven less than 300, so I subtracted 300 from 263 then added back seven. I would get answers faster than kids doing it the “right” way in columns, but got in trouble because I couldn’t “show my work”. I never did “get” algebra though, but the truth is 99% of folks never need more than simple arithmetic in real life.

Interestingly decades later my son got in trouble because he scored the highest they had seen on his AP math final, but had no work to show. They accused him of somehow getting a copy and cheating, though he told them he did it in his head. They agreed to let him take another test and he scored even higher, getting profuse apologies and a science scholarship.

[marktwain]

In their example, I knew that 293 was seven less than 300, so I subtracted 300 from 263 then added back seven.

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Yes, I did stuff like that as well.

Isaac Asimov wrote a whole book about those sort of tricks.

https://www.amazon.com/Quick-easy-math-Isaac-Asimov/dp/B0006BLVLA#customerReviews

[LeoTDB69]

"but got in trouble because I couldn’t “show my work”."

That comment made me remember this pic