This textbook is a third-grade course in arithmetic. It contains a review of the preceding book, a continuation and extension of the work in the fundamental processes and in fractions, and the introduction of several new principles in their simplest form, as percentage. The exercises are divided into lessons for convenience. Better results will follow if the order indicated here is quite closely followed; for it combines new principles, and review of old principles, in such a way as to make the advance more uniform and thorough.