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Unrelated, but relates to 9: if you take any two digit number,say 59, and you deduct the sum of the two digits 5 and 9, it yields 45, a multiple of 9. Interesti
by why-el 15y ago
Unrelated, but relates to 9: if you take any two digit number,say 59, and you deduct the sum of the two digits 5 and 9, it yields 45, a multiple of 9. Interestingly, this is true for any two digit number. I used this trick in a game where I labeled all multiples of 9 with a sign, asked my sister to perform the operation above, and claim that I can guess the sign, because all multiples of 9 share the same sign. :)
- rimantas 15y ago> Interestingly, this is true for any two digit number Not only for two digits numbers. Also there is a trick based on that: ask someone to think of a number (two-digits, or greater). Ask to subtract the sum of digits from that number. Ask to multiply result by any number. Ask to cross-out any digit, except 0 and then say remaining digits to you in any order. Then you say what digit was crossed out. The secret is simply: you add the digits told to you till you get one digit number, and then subtract it from nine. E.g.: Original number => 42 Subtract the sum => 42 - 6 = 36 Multiply by any number => 36 * 666 = 23 976 Cross out 3 => 2976 Name the digits in any order => 2679 So you got 2679. Calculate digital root: 2 + 6 + 7 + 9 = 24, 2 + 4 = 6. 9 - 6 = 3 <= there is your answer. See also: http://en.wikipedia.org/wiki/Digital_root http://en.wikipedia.org/wiki/Digital_root http://en.wikipedia.org/wiki/Casting_out_nines http://en.wikipedia.org/wiki/Casting_out_nines
- muyuu 15y agoActually this generalizes for all number of digits (down to 1) and to all multiples of 3, 9 or any number only divisible by 3. And it's not just an if, it's an iff. 132144 => 1+3+2+1+4+4 = 15 => 1+5 = 6 (divisible by 6 - obviously you can stop at 15 too)