I've seen people compute complex arithmetic off the top of their head. How do they do it? [more inside]
posted by Christ, what an asshole on Apr 30, 2009 - 13 answers

Is there an online or otherwise calculator utility that can produce a multiplication column to the nearest integer if I need to (and I do need to) multiply a given integer (specifically, 8.57143) by all the integers from 1 to about 600, displayed in a list so that I don't have to multiply it each time? I may need to do other 600-deep columns with other decimally numbers, a few at most. I need to see the result, better yet print it. [more inside]
posted by gorgor_balabala on Jul 10, 2008 - 18 answers

Faster techniques for grabbing lines of a file and doing text manipulation and arithmetic via shell (or other) scripting? [more inside]
posted by Blazecock Pileon on May 9, 2008 - 20 answers

ABC x D = BADC. What single numbers (1-9) do the letters represent? Is there any way to arrive at the answer (a) by logical deduction all the way rather than with some trial-and-error and (b) so that a 10-year-old can follow the logic? [more inside]
posted by londongeezer on Sep 16, 2007 - 15 answers