I saw a video of this triangle puzzle and could not find a 3D model for it, so I decided to make one with Tinkercad. In the unsolved state, there are 7 pieces forming a large triangle, and the challenge is to add another small triangle in a way that the 8 pieces still form a triangle that fits within the tray.

I recommend printing the triangle pieces in a single solid color because [Spoiler Alert #1] to solve the puzzle, some of the pieces may need to be flipped upside down. However, the tray can be printed using multiple colors if desired. This is easy to print without supports, and you can scale the size of the models, just make sure you scale the numbers and tray equally.

Spoiler Alert #2: Although there are many solutions to this puzzle, I’ve included a photo of one possible solution.

Note that I built some tolerance into the triangle pieces to make sure they’d fit in the tray. In retrospect, there is a little bit more space than I really needed, as you can see a little bit of wiggle room even in the solved state. You could probably proportionally scale up the size of the triangle pieces to 101% (i.e., X, Y, and Z axes) or possibly even more depending on the accuracy of your printer. It really depends on how tightly you want the pieces to fit in the tray. I’d appreciate posts of makes as well as the settings you used.

UPDATE: I found similar models so am providing links in case you like those versions more. They are “Triangle +” (https://www.thingiverse.com/thing:4978789) and “triangle double puzzle” (https://www.thingiverse.com/thing:6718494).