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.

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## About Jim Lawless

I've been programming computers for about 36 years ... 30 of that professionally. I've been a teacher, I've worked as a consultant, and have written articles here and there for publications like Dr. Dobbs Journal, The C/C++ Users Journal, Nuts and Volts, and others.

is there any formula to solve such puzzals?

i want sm formulas for my exams……..

None that I know of, although a friend and I began to discuss how to write a function that would allow a computer program to calculate the total number of triangles given the depth.