Why do this problem?
The main reason for using this problem is to encourage pupils to develop a system for finding all the possible arrangements. This is something that they might find difficult. So before tackling this problem, you may like to introduce your group to Triangle Animals
This is an ideal activity for pupils to work on in pairs and you can learn a lot about their mathematical understanding from listening to them talk. After allowing them time to have a go at this problem, it might be a good idea to draw the whole class together to ask how they are going to be sure that they've found all the different arrangements. At this point, some might have tried to implement
a system of their own. If they have, you could use this as a model for everyone, but it might be necessary for you to initiate such a system. For example, you could start by holding three of the triangles still and then move the fourth to different positions. At this stage, you might also want to address the issue of what arrangements are the same and what are different. It might be easier to
come to an agreement on this by not allowing "flips", for example.