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The number 9 has a unique quality within our base 10 number system. If you recursively add the digits for any multiple of the number 9 you will end up with the answer 9. For example:
9*38=342
3+4+2=9
9*154=1386
1+3+8+6=18
1+8=9
9*37652891=338876019
3+3+8+8+7+6+0+1+9=45
4+5=9
A similar rule applies to multiples of the number 3 although the final answer results in a 3 or a 6 which spoils the effect a little.
Can anyone give me an explanation for this behaviour? Its a shame 42 isn't a multiple of 9... could have lead to some interesting debates about whether 9 is really the answer!
9*38=342
3+4+2=9
9*154=1386
1+3+8+6=18
1+8=9
9*37652891=338876019
3+3+8+8+7+6+0+1+9=45
4+5=9
A similar rule applies to multiples of the number 3 although the final answer results in a 3 or a 6 which spoils the effect a little.
Can anyone give me an explanation for this behaviour? Its a shame 42 isn't a multiple of 9... could have lead to some interesting debates about whether 9 is really the answer!