Number 9 is an amazing number; if the number 9 is multiplied by any number of single-digit, after adding together the two digits of the product always get 9. For example: 9x3 = 27 = 2 + 7 = 9; 9x9 = 81 = 8 + 1 = 9; 9x5 = 45 = 4 + 5 = 9 and so forth.
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