K nex 78720 elementary math geometry set for 3 to 4 students k nex 78720 the k nex 78720 elementary maths and geometry set provides an introduction to 2d and 3d shapes symmetry and fractions for hands on maths p p the set contains 142 pieces to and builds 40 different 2d and 3d mathematics models multiple models can be built simultaneously making the set suitable for 3 to 4 students age 6 and above p k nex 78720 elementary math geometry