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This puzzle consists of counting ten triangles (check three sides for each one, remember that there aren't exist triangles with more than three sides :P ) using two straight lines that cross the figure wherever you want.

You can't count a triangle that contains other triangles inside. I mean, every triangle has to have an empty area inside. Here is an example of the game:

enter image description here

Is kind of easy to find nine triangles, but I only could find one solution that solves the problem. Good luck! Ask me if you don't understand the rules!

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  • $\begingroup$ So you have the star (with 5 triangles) and you need to add 2 lines in a way that there will be exactly 10 triangles? $\endgroup$ – klm123 Sep 22 '14 at 17:20
  • $\begingroup$ Is the star supposed to lack radial symmetry? $\endgroup$ – DrunkWolf Oct 19 '15 at 19:44
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I was starting to get disappointed, but finally I found the solution. here it is:

enter image description here

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  • 1
    $\begingroup$ Congratulations! It was really hard for me... I took me two days of thinking and trying. $\endgroup$ – Mauro Bilotti Sep 22 '14 at 19:19
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    $\begingroup$ Have you try looking for one more solution? The guy who introduce me this puzzle said that is another. $\endgroup$ – Mauro Bilotti Sep 22 '14 at 19:21
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    $\begingroup$ my solution came from yours, I knew that each line must increase the number of triangles by two and both lines have should make the last triangle, and this solution came to mind. another solution? let's try ;) $\endgroup$ – Rafe Sep 22 '14 at 19:33
  • $\begingroup$ Replace the lower line with a line through 9, 10, and the center pentagon which will also create four new triangles. $\endgroup$ – Ross Millikan Sep 23 '14 at 2:44
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    $\begingroup$ @MauroBilotti: I think it was the only solution. Please again with your guy. It would be great if you ask for that and post the other solution. thanks btw :) $\endgroup$ – Rafe Sep 24 '14 at 8:19

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