posted by Allysson .
How can 7 trees be planted so that there are 6 rows of trees in a straight line with each row having 3 trees?
Try a triangle with 3 trees on each side = 6 trees. Then put one tree in the middle of the triangle. The lines of three through the middle tree give you the remaining 3 rows. I cannot demonstrate it here, but you should be able to draw it yourself.
I hope this helps. Thanks for asking.