This is the answer to the NPR puzzle for Sunday, Nov 6, 2011.
The puzzle (and discussion on the answer) can be found here:
Q: Take 15 coins. Arrange them in an equilateral triangle with one coin at the top, two coins touching below, three coins below that, then four, then five. Remove the three coins at the corners so you're left with 12 coins. Using the centers of the 12 coins as points, how many equilateral triangles can you find by joining points with lines?
A: 25 equilateral triangles total (see the video for details):
13 small triangles pointing up or down
4 medium triangles pointing up or down
6 medium triangles pointing left or right
2 large triangles at a slight angle