> 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 (

> 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