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And 299999999 is divisible by 13 (lemmy.world)
submitted 1 month ago by m4m4m4m4@lemmy.world to c/science_memes@mander.xyz
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[-] TwilightKiddy@programming.dev 86 points 1 month ago

The divisability rule for 7 is that the difference of doubled last digit of a number and the remaining part of that number is divisible by 7.

E.g. 299'999 → 29'999 - 18 = 29'981 → 2'998 - 2 = 2'996 → 299 - 12 = 287 → 28 - 14 = 14 → 14 mod 7 = 0.

It's a very nasty divisibility rule. The one for 13 works in the same way, but instead of multiplying by 2, you multiply by 4. There are actually a couple of well-known rules for that, but these are the easiest to remember IMO.

[-] urda@lebowski.social 62 points 1 month ago

Thanks I hate it

[-] veroxii@aussie.zone 9 points 1 month ago

This math will not stand man!

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this post was submitted on 04 Nov 2024
682 points (97.8% liked)

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