| 摘要 |
This invention relates to an educational device having a card with notched edges and a series of numbers or words along each longitudinal edge of the card corresponding to each notch. The correct answer to a problem from one edge of the card, whether arithmetic or grammatical or historical, is found on the opposite edge of the card. A string member is used to connect the problem on one edge of the card with the correct answer on the other edge. The reverse side of the card has the correct string lines imprinted thereon corresponding to the correct placement of the string member for the correct answers to the problems on the face side of the card.
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