Puzzles
Work out the day of the week for any date in history, in your head, in seconds
What day of the week was 4 July 1776? Mathematician John Conway devised a mental algorithm, the Doomsday rule, that lets a practiced person answer questions like this for any date — past, present, or centuries into the future — using a handful of memorized 'anchor days' and simple arithmetic.
Reveal the answer
4 July 1776 was a Thursday. Conway's method finds each year's 'Doomsday' — a day of the week that several fixed dates, like 4/4, 6/6, 8/8, 10/10 and 12/12, always fall on within that year — then counts forward or back from whichever anchor date is nearest. With practice, Conway himself could answer in under two seconds.
— John Conway & Richard Guy, The Book of Numbers — Copernicus/Springer, 1996
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