How many triangles do you see in this image?

Ouadie Rhabbouron

You thought you had the right answer, and yet… this famous puzzle trips up more than one expert eye! At first glance, you count a few triangles, then you add them up as you progress through the “levels.” Simple? Not quite. The figure—a large triangle divided by three lines parallel to its base—conceals more shapes than you might imagine. Ready to outsmart the trick and shine at your next quiz night? Follow the guide.

The Hidden Triangles Trap

Our brain loves to spot the obvious little triangles and… forget the large ones that are formed by combining several areas. The result: we underestimate. In the classic configuration (4 rows formed by 3 lines parallel to the base), the correct answer is  27. If
you found 26, you most likely missed a large composite triangle—often an upward-pointing triangle that extends over 3 levels, or a "half-wide" triangle on one side.

Step-by-step method: counting without making mistakes

Identify the "upward" triangles according to their height:

  • Height 1 level: 10
  • Height 2 levels: 6
  • Height 3 levels: 3
  • Height 4 levels: 1

Subtotal “upwards”: 10 + 6 + 3 + 1 = 20.

Add the "downward" triangles resulting from the nesting of the segments: 7.

Total: 20 + 7 = 27.
Mnemonic tip: think “20 ​​at the top + 7 at the bottom” and you will avoid the classic forgetfulness.

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