This problem was a little more difficult that it looked, I think.
We had some suggestions that the three groups should be right-angled triangles, equilateral triangles and isosceles triangles. I'm not sure that any of the triangles are equilateral. How do I know?
Emily from said St James School told us:
You're right, Emily, thank you. Beatrice from Raffles Girls' School in Singapore sent in a picture of the completed groups:
Cong, from St Peter's RC Primary also sent us an image of his solution:
I think that each one of you has put just one triangle in the wrong place. I wonder whether you can spot which one it is in each picture?
Well done all of you!