After having some fun with the squares puzzle posted on Facebook, I saw this one tonight. It asked how many triangles are there in the picture. Options are 9, 10, 11, 12, and 13.
I see 13. Here’s how I arrived at my answer.
There are 9 small triangles in the interior ( alternately colored red and yellow below):
There are three larger triangles in the interior:
That brings us to 12 ( 9+3 ). The entire puzzle is also a triangle.
That brings us to 13.