This work is related to the study of divisibility by nine. The application of the Nine Proof is more of a game of mental exercise than a precise Control of Error. However, when presenting this material to the students, they are often fascinated by it. Any time students practice the four operations, either in the concrete or the abstract, the Nine Proof can be used as a method of probable verification. The game of the Nine Proof is especially captivating when it is applied to multiplication and division.
Includes: Ten exercises each for addition, subtraction, multiplication, and division. One Booklet for Instructions & Control. One four-part diagram card + numerals.