The 9 number thing is called the digital root system, and happens because you are using base 10 numbers. This happens due to the digital root counting up by (10 - 1)n with each multiple of 9 and 9 counting up (10-1)n with each multiple in the digital root. Basically when you are summing you are adding the base 10 and subtracting 1, which is 9.
Simpler tricks also impress people. I blew an accountant friends mind the other day when we were talking about how we work out operations on numbers, by telling him 18% of 50 is the same as 50% of 18 etc.
Simpler tricks also impress people. I blew an accountant friends mind the other day when we were talking about how we work out operations on numbers, by telling him 18% of 50 is the same as 50% of 18 etc.
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