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Magic Rods (Posted on 2003-11-11) Difficulty: 4 of 5
You need to make a set of five rods for a magic trick, with numbers on them ranging from 1 to 31 inclusive. Then you ask people to pick a number and show you only the top number of whatever rods it is on. From that you have to guess which number the person picked. This has to be done within a few seconds and isn't a matter of remembering what numbers are on them.

What numbers should be on each of the five rods?

  Submitted by Lewis    
Rating: 4.0000 (7 votes)
Solution: (Hide)
The numbers should be:

Rod 1: 1,3,5,7,9,11,13,15,17,19,21,23,25,27,29,31

Rod 2: 2,3,6,7,10,11,14,15,18,19,22,23,26,27,30,31

Rod 3: 4,5,6,7,12,13,14,15,20,21,22,23,28,29,30,31

Rod 4: 8,9,10,11,12,13,14,15,24,25,26,27,28,29,30,31

Rod 5: 16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31

This uses the same idea as the binary system. All you do is add up the first numbers of the rods that have the number on. It works becuase the first number of each rod are 1,2,4,8 & 16, and using those numbers you can make any numbers from 1 to 31. For example, to make 25 you use the numbers 1,8 and 16, which are rods 1,4 and 5, so 25 is only written on those three rods.

Comments: ( You must be logged in to post comments.)
  Subject Author Date
Solution hereChristopher Kostelec2003-12-15 23:01:10
My solutionDavid Hanna2003-12-03 20:59:41
SolutionSolutionpaige2003-11-26 23:29:34
Why so complicated?Nelson2003-11-12 03:22:57
re: The top number?Dan2003-11-12 02:58:35
SolutionSpare the rod, spoil the magicianDan2003-11-12 02:39:32
SolutionsolutionTristan2003-11-11 18:59:48
re: The top number?SilverKnight2003-11-11 15:55:29
ClueS2003-11-11 15:45:16
SolutionThe top number?Charlie2003-11-11 15:40:32
Some Thoughtsever so slight improvementLee2003-11-11 15:03:54
re: Full SolutionSilverKnight2003-11-11 13:45:34
SolutionFull SolutionSilverKnight2003-11-11 13:42:45
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