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CONSIDERING THE RECENT INTEREST in proof by nines, one might conclude this is a mid-twentieth century discovery. Probably we can concede it is a rediscovery. In University Arithmetic by Charles Davies, LL.D., A. S. Barnes & Co., New York, 1868, the process is explained and is used throughout the book. In Advanced Arithmetic, Teachers Edit ion, G. A. Wentworth, Ginn & Co., Boston, 1898, the check by nines is called for and no explanation given, indicating it was expected to be part of a teacher's store of arithmetic knowledge.doi:10.5951/at.3.5.0204 fatcat:5mu3rigkyjfzra4tdr3hbs7zpa