AoPS is a good idea; you can try their Introduction and Intermediate volumes (algebra, geometry, combo, number theory) which are around AMC/AIME level. There are other volumes of books but I’m not as familiar with them.
AoPS is a good idea; you can try their Introduction and Intermediate volumes (algebra, geometry, combo, number theory) which are around AMC/AIME level. There are other volumes of books but I’m not as familiar with them.