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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.

Today, Perhaps More Than ever before, we at least pay lip service to teaching for understanding in arithmetic. Too often, however, this “ understanding” still implies mere knowledge of how to perform a mechanical process. Checking any one of the four processes of arithmetic by casting out of nines is a good illustration of this fact; though, occasionally some wide awake boy or girl in junior high school arithmetic challenges the teacher by asking such questions as: “Why does it work?” “Will it work with any other number?” These are good, intelligent questions, but questions which many teachers who feel rather secure in teaching most of the arithmetic find difficulty in answering. And yet, at least partial answers are understandable, interesting and challenging to pupils.