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Secret Code (Posted on 2005-03-10) Difficulty: 2 of 5
An intellingence agency wants to have codes. For this it uses two digit natural numbers such that the two digits are different. Each of these codes are written on different sheets of paper so as to be used. However, the director of the agency soon realizes that many codes are not uniquely recognisable.
For example, 61 and 19 is one such pair because when the sheet of paper is read upside down, a different number may be read. However, 01 is invalid (no leading zeroes).

How many useful codes are there that the agency can use?
Note: The only digits that make sense when inverted are 0,1,6,8 and 9.

See The Solution Submitted by Sandeep    
Rating: 2.3333 (9 votes)

Comments: ( You must be logged in to post comments.)
  Subject Author Date
SolutionSolutionDej Mar2008-07-06 21:17:01
is this okay?sean2005-08-29 01:37:51
Is this right?Brandon2005-05-21 15:25:20
Solution?Jeff2005-05-12 20:06:11
re: solution i thinkjo2005-05-02 06:35:07
solution i thinkjo2005-05-02 06:34:43
solution i thinkjo2005-05-02 06:34:23
SolutionSolutionRick2005-05-02 03:30:56
re: my answergary wallravin2005-04-17 07:00:29
re: SolutionEddy Karat2005-04-15 23:20:29
SolutionSolutionRupesh Khandelwal2005-04-14 14:31:42
SolutionsolutionEddy Karat2005-04-13 22:25:00
Solutionmy final answerTeresa2005-04-13 06:00:06
my best answerTeresa2005-04-13 05:54:31
my answerTeresa2005-04-13 05:48:22
re(2): No Subjectgary wallravin2005-04-09 23:45:26
re: No Subjectjohn2005-04-06 15:59:06
re(2): venkat vgary wallravin2005-04-06 01:14:45
re: solutionvenkat v2005-04-04 19:24:13
Solutionsolutiongary wallravin2005-03-20 22:35:25
Solutionthe answer is 83 shown in detailmark2005-03-18 20:35:14
re: No Subjectrachael2005-03-18 02:51:07
No Subjectrachael2005-03-18 02:47:24
Questionam I right?Rex2005-03-12 08:10:48
SolutionSachin2005-03-11 04:21:58
I am wrongSachin2005-03-11 04:13:55
Errata Solution with explaination (may be a spoilerSachin2005-03-11 04:11:54
Solution with explaination (may be a spoiler)Sachin2005-03-11 04:00:11
re(2): Solution?Timothy Bard2005-03-10 17:46:58
69 and 96Jeff Manners2005-03-10 15:55:07
Solutionre: Solution?Erik O.2005-03-10 14:14:54
SolutionSolution?Timothy Bard2005-03-10 14:04:12
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