A triangle-counting puzzle like the one in the image looks easy at first—until you start noticing triangles hiding inside triangles. This type of brain teaser goes viral because our eyes tend to lock onto the smallest shapes and miss the larger ones formed by combining multiple small sections.
The drawing shows a large equilateral triangle subdivided into a neat triangular grid. That grid creates triangles in two orientations (pointing up and pointing down) and in multiple sizes.
The Biggest Mistake People Make
Most people count only the tiniest triangles. But the real total comes from adding:
- Small triangles
- Medium triangles made of 4 small ones
- Larger triangles made of 9 small ones
- The single largest outer triangle
If you skip sizes, your answer will be too low.
The Correct Count
After counting every triangle of every size, the correct total is: