Seems to be based on the old accounting trick that when you're summing a bunch of numbers, if the difference between the answer you got and the one you wanted to get is divisible by nine, you must have transposed some digits. By making use of the old divisibility trick that if a number's digits add up to a number that is divisible by nine, the number is divisible by nine, you can find the number at the end merely by adding up the digits you type in and subtract that from the next highest multiple of nine
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Seems to be based on the old accounting trick that when you're summing a bunch of numbers, if the difference between the answer you got and the one you wanted to get is divisible by nine, you must have transposed some digits. By making use of the old divisibility trick that if a number's digits add up to a number that is divisible by nine, the number is divisible by nine, you can find the number at the end merely by adding up the digits you type in and subtract that from the next highest multiple of nine
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