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a quick math challenge
12-31-2013, 03:03 PM
Post: #13
Curlytop Offline
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RE: a quick math challenge
(12-29-2013 06:31 PM)aurelio Wrote:  a bit more difficult the divisibility by 7
Similar 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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Messages In This Thread
a quick math challenge - Don Shepherd - 12-27-2013, 05:03 AM
RE: a quick math challenge - Han - 12-27-2013, 05:12 AM
RE: a quick math challenge - Don Shepherd - 12-27-2013, 12:47 PM
RE: a quick math challenge - Don Shepherd - 12-27-2013, 04:43 PM
RE: a quick math challenge - Paul Dale - 12-27-2013, 10:53 PM
RE: a quick math challenge - Les_Koller - 12-28-2013, 10:06 PM
RE: a quick math challenge - Waon Shinyoe - 12-29-2013, 02:19 PM
RE: a quick math challenge - Thomas Klemm - 12-29-2013, 03:37 PM
RE: a quick math challenge - aurelio - 12-29-2013, 06:31 PM
RE: a quick math challenge - Curlytop - 12-31-2013 03:03 PM
RE: a quick math challenge - Thomas Klemm - 12-31-2013, 05:38 PM
RE: a quick math challenge - Curlytop - 12-31-2013, 03:05 PM
RE: a quick math challenge - Curlytop - 12-31-2013, 07:25 PM



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