COMMON SCHOOL ARITHMETIC. OF NUMBERS. ARTICLE 1. A UNIT is any single thing, as an orange, an apple, a dollar, etc. ART. 2. A NUMBER is a unit, or a collection of units; one pound is a unit; five pounds is a collection of units. ART. 3. ARITHMETIC is the science of numbers. It teaches us how to use numbers in making calculations. ART. 4. Numbers may be expressed in several ways-by words, by letters or by figures. In arithmetic, numbers are usually expressed by figures. ART. 6. NUMERATION is the art of reading numbers after they have been written. ART. 7. Two methods of Notation are in general use, the Arabic and the Roman. ARABIC NOTATION. ART. 8. The ARABIC Notation was introduced into Europe from Arabia in the tenth century. To express numbers, it uses ten different characters, called figures, viz. : 9 |