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 Secret Code (Posted on 2005-03-10)
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)

 Subject Author Date Solution Dej Mar 2008-07-06 21:17:01 is this okay? sean 2005-08-29 01:37:51 Is this right? Brandon 2005-05-21 15:25:20 Solution? Jeff 2005-05-12 20:06:11 re: solution i think jo 2005-05-02 06:35:07 solution i think jo 2005-05-02 06:34:43 solution i think jo 2005-05-02 06:34:23 Solution Rick 2005-05-02 03:30:56 re: my answer gary wallravin 2005-04-17 07:00:29 re: Solution Eddy Karat 2005-04-15 23:20:29 Solution Rupesh Khandelwal 2005-04-14 14:31:42 solution Eddy Karat 2005-04-13 22:25:00 my final answer Teresa 2005-04-13 06:00:06 my best answer Teresa 2005-04-13 05:54:31 my answer Teresa 2005-04-13 05:48:22 re(2): No Subject gary wallravin 2005-04-09 23:45:26 re: No Subject john 2005-04-06 15:59:06 re(2): venkat v gary wallravin 2005-04-06 01:14:45 re: solution venkat v 2005-04-04 19:24:13 solution gary wallravin 2005-03-20 22:35:25 the answer is 83 shown in detail mark 2005-03-18 20:35:14 re: No Subject rachael 2005-03-18 02:51:07 No Subject rachael 2005-03-18 02:47:24 am I right? Rex 2005-03-12 08:10:48 Solution Sachin 2005-03-11 04:21:58 I am wrong Sachin 2005-03-11 04:13:55 Errata Solution with explaination (may be a spoiler Sachin 2005-03-11 04:11:54 Solution with explaination (may be a spoiler) Sachin 2005-03-11 04:00:11 re(2): Solution? Timothy Bard 2005-03-10 17:46:58 69 and 96 Jeff Manners 2005-03-10 15:55:07 re: Solution? Erik O. 2005-03-10 14:14:54 Solution? Timothy Bard 2005-03-10 14:04:12

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