Abstract: A didactic-educational toy for elementary arithmetic operations includes a plurality of transparent plates. Each of the transparent plates has ten circular orifices. The orifices are distributed symmetrically in two rows. Each row has five of the orifices. Each of the orifices has substantially the same diameter. A plurality of plates each has cylindrical stepped protuberances. Each of the protuberances has a base with a diameter corresponding to a diameter of the orifices of the transparent plates to provide for close-fitting insertion of the base into a corresponding one of the orifices. Each of the protuberances has an upper portion having a diameter smaller than the diameter of its base to facilitate the insertion of the protuberance into a corresponding orifice. The plurality of plates, which have cylindrical stepped protuberances include plates has a different number of protuberances. The surface area of each plate is substantially proportional to the number of protuberances.