ab wrote:You can convert each 3 into a 4 by halving a green, yellow or red triangle, which gives 9 options
I totally missed those.
ab wrote:... but you can also convert each 2 into a 4 by making one of the two triangles into a 3 which gives rise to 2 more
But you can do that to each triangle two different ways. And you can make two triangles out of each of the two triangles. Which is what I counted to arrive at my (crappy) answer of 5.
But (I think) each of those 5 is identical to 1 of your 9.
[edit: And Ruud finds a 10th by thinking "outside the triangle"

... and dividing the 90 degree angle by 3. Cool!]