a quick math challenge
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12-31-2013, 03:03 PM
Post: #13
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RE: a quick math challenge
(12-29-2013 06:31 PM)aurelio Wrote: a bit more difficult the divisibility by 7Similar to divisibility by 11, but you pair the digits off into threes before checking them out. Is 123,456,789 divisible by 7? Well, 123 - 456 + 789 = 456 which is not a multiple of 7, so neither is the original number. Can anybody explain why this works for 7 (and 13)? |
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