The puzzle is as follows [with minor copy edits for grammar]:
By only using matchsticks of equal length a set of equilateral triangles has been built as indicated in the figure from below. With that information, what is the minimum number of matchsticks that must be removed so that there aren't any of those triangles?
The alternatives given are:
This seems to be a variation of the typical puzzle involving the construction of a certain figure, as the task here is to delete the triangles.
I tried all sorts of combinations in removing the matchsticks, and my answers keep being off by one.
Since I'm not very good at this, could someone show me with a way to solve this sort of puzzle without much fuss?
My first guess was to remove systematically all the sides, but this would require moving many matchsticks. Then I thought to remove only the critical ones.
This is a matter of several trials. Needless to say that I ended up removing more than what the alternatives say.
Perhaps someone with more experience than me at solving this sort of puzzle could provide a strategy on where to look for removals first?
As I mentioned removing the edges of the hexagon inside don't help much and removing the exterior matchsticks also don't help as it increases the number.
What's the trick here? It would help me if answers included a drawing so I could understand the necessary removals.
This was obtained from my Puzzle challenges book which from its looks seems to be an adaptation from an IQ test from APA exams of the 1980s.