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Mirror, Mirror on the wall (Posted on 2004-07-15) Difficulty: 3 of 5
Find the lowest positive integer that has its digits reversed after dividing it by 2.

  Submitted by SilverKnight    
Rating: 2.0000 (2 votes)
Solution: (Hide)
There is none.

Assume there's such a positive integer x such that x/2=y and y is the reverse of x.

Then x=2y. Let x = a...b, then y = b...a, and:

         b...a   (y)
       x     2
      --------
         a...b   (x)
From the last digit b of x, we have b = 2a (mod 10), the possible values for b are 2, 4, 6, 8 and hence possible values for (a, b) are (1,2), (6,2), (2,4), (7,4), (3,6), (8,6), (4,8), (9,8).

From the first digit a of x, we have a = 2b or a = 2b+1. None of the above pairs satisfy this condition. A contradiction.

Hence there's no such integer.

Comments: ( You must be logged in to post comments.)
  Subject Author Date
SolutionPuzzle SolutionK Sengupta2008-06-04 00:42:48
AnswerK Sengupta2008-05-31 15:50:17
Solutionre: SolutionCharlie2004-07-15 23:06:27
SolutionSolutionTristan2004-07-15 18:02:17
Some ThoughtsNo Solution?DJ2004-07-15 17:45:21
Some ThoughtscomputerCharlie2004-07-15 11:18:31
Grasping at strawsSing4TheDay2004-07-15 10:41:32
SolutionSolutionEric2004-07-15 09:11:59
Some ThoughtsthoughtsCharlie2004-07-15 09:03:04
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