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Old 08-26-2016, 04:01 AM
Indistinguishable Indistinguishable is offline
Join Date: Apr 2007
Posts: 10,525
As for the second example, suppose we have the three digit number ABC with smaller reverse CBA. Since this is smaller, it must be that C < A. Subtracting the smaller from the larger gives us (A - C)0(C - A). Except C is less than A, so there must be a borrow for the last digit's subtraction: we actually get (A - C - 1)9(10 + C - A). Finally, adding this to its reverse gives 9(9 + 9)9 = 1089.

Last edited by Indistinguishable; 08-26-2016 at 04:01 AM.