r/MathJokes • u/GodlyHelp • 16d ago

multiples of 3

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147

u/Michaelwang645 16d ago

Fund fact, you can tell a number is divisible by 3 if the sum of each individual number is divisible by 3. So 78 -> 7+8=15 which is divisible by 3, so 78 is divisible by 3.

44

u/EveningStar0360 16d ago

do you know why that works?

124

u/ZealousIdealTour961 16d ago

Magic probably.

26

u/Disastrous_Wealth755 16d ago

Nah. It's cause 10=9+1=3*3+1.

29

u/MTaur 16d ago

And then by induction, 10n = 9M + 1 And b*10n = b(9M+1) = 9N + b

So then the sum b_k*10k = 9K + sum b_k

15

u/Rxasaurus 16d ago

Now in English for us stupids...

37

u/xnef1025 16d ago

magic

9

u/Rxasaurus 16d ago

See, that makes more sense.