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43I hands of a competent teacher, but which do require correction. For example the statement is made that selling by mail-order houses costs 7. 2I per cent of net sales, while the reviewer is sure that if he understands the statement, the figure should be something like three times as large. Again the statement is made that transportation charges on most manufactured products are not of special importance. Surely the following statement is incorrect: "In general the margin between thedoi:10.1086/253361 fatcat:a63cy7ukljagdiosatxhbrfhpe