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Twice the Sum of Its Digits

What number is twice the sum of it’s digits?

18.

1 + 8 = 9
2 × 9 = 18

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1 Comment on "Twice the Sum of Its Digits"


Greg says
July 28, 2020 @ 19:12

What number is 3 times the sum of it’s digits? 4 times? 5 times? 6 times?

Here’s a hint: all single digit multiples of 9’s digits (except 0) add up to 9, it even works as far as 10*9, but starts to fall apart after 11, but if you keep summing the digits, it will always go back to nine in the most reduced form regardless of the multiplier.
(11*9 = 99, 9+9=18, 1+8=9)
(73*9 = 657, 6+5+7=18, 1+8=9)
(654321*9 = 5888889, 5+8+8+8+8+8+9=54, 5+4=9)

This is a quick math trick to determine if a number is evenly divisible by 9, anything that distills back to 3, 6, or 9 is evenly divisible by 3


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