Something I told 14 yo: Good math tests have some problems to test whether you truly understand the subject. Often they'd take impossibly long to solve mechanic... (opens in new tab)

Something I told 14 yo: Good math tests have some problems to test whether you truly understand the subject. Often they'd take impossibly long to solve mechanically, but are easy once you see some trick. So if you encounter an apparently impossible problem, look for the trick.