Reminds me of yet another cool story from Richard Feynman about beating an abacus salesman with mental arithmetic: <a href="http:&#x2F;&#x2F;www.ee.ryerson.ca&#x2F;~elf&#x2F;abacus&#x2F;feynman.html" rel="nofollow">http:&#x2F;&#x2F;www.ee.ryerson.ca&#x2F;~elf&#x2F;abacus&#x2F;feynman.html</a>