| 摘要 |
A teaching device comprising a group of balls, a first counter, a second counter and a tray interconnecting the first counter to the second. The first counter represents the problem to be solved, and the second counter indicates the solution to the problem. Both counters include several parallel columns for holding several of the balls in a line, and a stop for at least one of the columns to limit the number of balls that can be held by that column. The tray is placed below the first counter so that balls placed in the first counter may be dumped into the tray by removing the stops from the columns of the first counter, and then pushed or allowed to fall from the tray into the second counter.
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