The Singapore Mathematics Curriculum includes 13 heuristics (of which 11 are for primary school) that teachers are supposed to train their pupils for use in mathematical problem solving. For convenient reference, this article lists these heuristics and some others, most of which are from my personal learning and teaching experiences (and a few by searching the Internet). Making observations, connecting facts and using heuristics to solve problems is part of a good mathematics education. Actually, there is nothing to stop a primary school pupil from using the more advanced heuristics, it is just that pupils should at least be taught the 11 listed.
· Think of the opposite problem (~H12)