Place 9 balls ("o") in the intersections of the grid below to achieve 10 straight lines, each line containing 3 and exactly 3 balls. You may assume, if you need, that each cell is a perfect square.

           +---+---+---+---+---+---+---+---+
           |   |   |   |   |   |   |   |   |
           +---+---+---+---+---+---+---+---+
           |   |   |   |   |   |   |   |   |
           +---+---+---+---+---+---+---+---+
           |   |   |   |   |   |   |   |   |
           +---+---+---+---+---+---+---+---+
           |   |   |   |   |   |   |   |   |
           +---+---+---+---+---+---+---+---+
           |   |   |   |   |   |   |   |   |
           +---+---+---+---+---+---+---+---+
           |   |   |   |   |   |   |   |   |
           +---+---+---+---+---+---+---+---+

Catullus had it right in the original: risibility trumps nescience (if we must choose).

I am sure it is difficult to anticipate all of the ways a reader might fail to discern the intention in a puzzle formulation.  Better to take a few more words, and perhaps try out the puzzle on some before posting.  One of the worst errors in info tech is to try to program a solution before you know what the ultimate users really want -- a huge time waster.

You may be familiar with Kordemsky's book "The Moscow Puzzles" (trsl. by Martin Gardner c 1972) which has a number of puzzles very similar to yours. He (or perhaps Gardner) tries to be explicit when using (e.g.) "lines".

Even the English when donning their garters resort to the bon mot -- honi soit qui mal y pense.   So, ad astra...

 

Posted by ed bottemiller on 2008-10-16 10:37:36