Reply #22: very good for him to figure this out. Is something evenly divisible by 3? Multiplying by 9.... [View All]

[uppityperson]

To find out if something is evenly divisible by 3, add up all the numbers in a number, keep doing so until you end up with 1 number. If it is 3, 6, or 9, it is evenly divisible by 3.
Example: 13,403,204,766. Add up each individual # to get 36. Add up 3+6=9. Yes, this number is evenly divisible by 3.

I use it for smaller numbers in daily use, but it works for all.

9's are great. Notice the right hand numbers. First one goes 012345678, the second goes 987654321. AND if you add up the right hand numbers, they equal 9. (0+9, 1+8, 2+7,etc).
9X1=09
9X2=18
9X3=27
9X4=36
9X5=45
9X6=54
9X7=63
9X8=72
9X9=81