Sticky triangles !!!
Table
No. of shape No. of triangles No. of matchsticks
1 1 3
2 4 9
3 9 18
4 16 24
5 25 30
6 36 56
7 49 67
The rules
All of the numbers of triangles are square numbers.
The rule for the number of matchsticks is that all of the no. are in the three times table ,i.e. if you have 64 triangles you would have 108 matchsticks.
5x5=25x2=50 divided by 4/10{2/5}=30 which makes the answer.