This problem offers children the opportunity to recognise, make and describe repeating patterns of triangles, and then challenges them to create repeating patterns of their own.
Using cut out triangles on the floor, or stuck to the board, you could begin to make the first pattern for the group to see. Ask children to work in pairs to make the same pattern and continue it, using cut out coloured triangles. (You may like to print off these sheets of the triangles onto coloured paper or card.)
Invite one pair to come to the board to continue the pattern and discuss with the whole class how they knew what to do. Encourage children to articulate the repetition of the two yellow and two green triangles making a rectangle. (Referring to the colours of the shapes rather than their names may be more appropriate for some.) Listen out for different ways of describing the repetition - there is not just one "right" way.
A plenary could consist of sharing a few of the class' patterns, again focusing on how we know how to continue them. You could do this by starting the pattern and then continuing it wrongly, to see whether the children can correct you.
Can you tell me about the pattern?
How would you carry on this pattern?
How do you know?
Children could be offered other shapes to use in creating patterns in addition to the two triangles here. For example, a triangle which is half the size of each could be used as well.
Some children might find it helpful to have more examples of patterns to continue before creating their own.