An old man, with four sons and three daughters, buried a safebox with valuables inside. He wanted his children to get it when he died, but neither the boys nor the girls to get it all for themselves; he desired that at least two sons and two daughters had to be involved in order to find the missing treasure.

(For example, the three girls on their own couldn't find the treasure, even if one boy helped them. The four boys and one girl couldn't find it either.)

How could he manage this?

My memory was not good.
The old man made 7 instructions. He had 4 of them assigned to the boys such that each had a unique triple.  To the girls he assigned 3 instructions with each having a unique pair.
Any two boys would therefore have a full set of 4 instructions between them.  Similarly any 2 girls would have a full set of 3.

Boys                           Girls
     1   2   3    4            1   2   3
A   x   x   x              P  x   x
B   x   x         x        Q  x        x
C   x        x    x        R      x    x
D        x   x    x

Any two boys Plus Any two girls = a full set of 7 instructions.
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I added this comment below the line after I saw Ken's comment.  We have the same basic concept.  While encryption was not specified, it is a valid option for the old man.

Edited on July 17, 2005, 1:09 pm

Posted by brianjn on 2005-07-17 07:02:49