The Triangles Puzzle

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:

t4 t2 t3

That brings us to 12 ( 9+3 ).  The entire puzzle is also a triangle.

That brings us to 13.


About Jim Lawless

I've been programming computers for about 38 years ... 32 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.
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2 Responses to The Triangles Puzzle

  1. Sauvik says:

    is there any formula to solve such puzzals?
    i want sm formulas for my exams……..

    • Jim Lawless says:

      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.

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