How to become a Lightning Calculator by Anonymous is part of the HackerNoon Books Series. You can jump to any chapter in this book here. Proof of Multiplication in Ten Seconds.
Proof of Multiplication in Ten Seconds.
The unitate of a number is the sum of its digits reduced to a unit.
The unitate of the multiplier is 9 and the unitate of the multiplicand is 6; 6 times 9 equals 54, and the unitate of 54 is 9. Now the unitate of the product is found to be 9 also, which is a proof of the correctness of the work.
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This book is part of the public domain. Anonymous (2021). How to become a lightning calculator. Urbana, Illinois: Project Gutenberg. Retrieved https://www.gutenberg.org/cache/epub/65078/pg65078-images.html
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