Math
posted by Helen .
farmer has 10 trees see if you can plant them so there are 5 rows of trees with 4 trees in each row

Am I missing something? five rows of four trees each is 20 trees.

Yes, this is one of those little teasers where you have to think outside the box. Arrange the trees in a pentagram. There are 5 trees at the vertices, and 5 more where the diagonals intersect. So, draw the lines and you'll see you have 5 intersecting lines, each with 4 trees. Each tree is counted twice.