Abstract: Apparatus for teaching mathematics has numerical and mathematical operational inputs by way of coded cards placed in respective card readers and a keypad that produces number values and numerical equations. The number values and equation results are compared to the numeric value of weight objects placed on a scale by the student. The apparatus is bi-directional in that unit weights are placed on the scale to attempt to match the numeric values and the equation solution values produced by the cards and keypad or the cards and keypad entries for numerical values and equations are made to match the numeric value of the unit weight objects on the scale. The student is informed of the result of the comparison in terms of correct or incorrect, or by explanatory messages to either increase or decrease the unit weight value or change the number value or the equation.

Abstract: A three dimensional polyhedron frame structure formed by a plurality of rigid rods and a plurality of hubs in which each rod has a retractable bolt at at least one end for assembly into a socket of a hub having a plurality of sockets that accept a plurality of rods with the rods being assembled to the hubs in different directions to form frames of various polyhedron shapes. A board is attached to at least one horizontal rod forming a vertical face of a prism frame so that its angle of inclination can be adjusted to demonstrate a principle of gravity. Preferably the rods are electrically conductive and the hubs are non-conductive so that wires can be connected to selected rods to form an electrical circuit.