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## Main Question or Discussion Point

Take any whole number and add the digits down to a single number. Now, subtract this number from the original number. With this answer add the digits down to a single number and it will always end up being 9.

Example: 22 (2+2=4) 22-4=18 (1+8=9)

or

14567 (1+4+5+6+7=23 and 2+3=5) 14567-5=14562 (1+4+5+6+2=18 and 1+8=9)

Why does you always end up with 9 and is there a name for this?

Example: 22 (2+2=4) 22-4=18 (1+8=9)

or

14567 (1+4+5+6+7=23 and 2+3=5) 14567-5=14562 (1+4+5+6+2=18 and 1+8=9)

Why does you always end up with 9 and is there a name for this?