each card is 2.1 in x 1.8 in x 0.12 in / 5.4 cm x 4.5 cm x 0.3
6 hardwood cards have a different number lasered on each side (12 different numbers total). You, as the Wizard, will be able to quickly predict the sum of the numbers lying face up on the cards as arranged by a spectator.
Have someone arrange the cards in any order and add the numbers facing up without you seeing. Then ask them to simply tell you (or optionally write down) only the shapes surrounding the numbers. Upon hearing the shapes, you will be able to almost immediately tell them tell them answer. Really quite amazing!
Each card measures 2.2" x 1.75" x 1/8" thick and is made from State of Maine Hardwoods. May be maple, cherry, or birch used. The math required to solve is modest, and I suspect most 10 year olds would be capable, and some younger depending on ability.