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Triangular truss brainteaser

By , 25 November 2020

By Rok Willesee

Difficulty: Fun

An engineer has asked you to help him count the number of triangles in this roof truss. He thinks there are five, but his boss thinks there are more. How many triangles can you see?

Triangle divided into multiple triangles.

Credit: CSIRO/Diya Dhaliwal

Scroll down or click for a hint, or the answer!


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Brainteaser hint

Small triangles together can make bigger triangles.

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Brainteaser answer

When counting shapes, it’s important to keep organised. Let’s count the triangles in groups, based on size:

• There are four small triangles, near the top.
• There are two medium sized triangles. One is at the bottom right, and the other surrounds the four small triangles.
• The whole truss makes up one big triangle.

All together, there are 4 + 2 + 1 = 7 triangles.

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