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Lizzie came up with a divisibility test for a certain number :

Break a positive integer  into two-digit chunks, starting from the ones place.

Find the alternating sum of these two-digit numbers, by adding the first number, subtracting the second, adding the third, and so on.

Find  and show that this is indeed a divisibility test for m.

 Feb 21, 2021
edited by Guest  Feb 21, 2021

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