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Originally Posted by MichaelFarker
My favorite fact about numbers deals with multiplying 9's. Look at 4x9=36, 5x9=45, 6x9=54, 7x9=63 ... The first digit of the answer is your 9's target minus one (4-1=3 for 4x9=36). Then the second digit of the answer is the number needed to make the answer add up to 9 (3+6=9 for 4x9=36).
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Edit: oops, read it again and you had the sums=9. Another way to look at it any multiplier of 9 will equal a factor(or multiple) of 9 when the sum's digits are added together. 9x31=279, 2+7+9=18, 1+8=9.
Anything multiplied by 5 is half the multiplier x10. Ex: 5x36=180, 5x130=650, 5x112=560, etc.
