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also, back to the 9 trick:
For numbers 0-10, whatever you multiply by 9, subtract 1 from it and you have the first number. 11-20, subtract 2. 21-30, subtract 3, and so on. You now have all but the last number of the answer. The final number is whatever makes the string of numbers add up to 9. This works up to 150.
ie.
9x6:
6-1 = 5
first number = 5
5+4=9
answer = 54
longer example: 9x150
150-15 = 135
1+3+5=9 so the final digit is 0.
9x150=1350
btw, the "digits add up to 9" trick sort of breaks down over 150 for awhile, and the digits add up to 9x2, or 18:
151x9 = 1359
1+3+5+9=18
185x9=1665
1+6+6+5 = 18
etc etc
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