How can you plant seven straight rows of trees with six trees per row such that twenty-one trees are planted in total?

How can you plant nine straight rows of trees with three trees per row such that nine trees are planted in total?

What about this?

Plant three trees such that they form a large equilateral triangle.

At the midpoint of each side of the large equilateral triangle, plant a tree.  These 3 new trees form a small equilateral triangle.

At the midpoint of each side of the small equilateral triangle, plant a tree.

And now there are 9 rows of 3 trees, using 9 trees.  Along each side of the large equilateral triangle, there are 3 trees.  Along each side of the small equilateral triangle, there are 3 trees.  And then if you draw a line from the vertex of the large triangle to the midpoint of the opposite side of the large triangle, it will pass through 3 trees.

Posted by nikki on 2006-11-10 18:08:15