tem to contend with, including at least three different types of arithmetic: finger-reck-
oning arithmetic (counting on fingers), a sexagesimal system with numbers written in
letters of the Arabic alphabet, and Indian numeral arithmetic.
The evolution of the Hindu-Arabic numbers continued throughout time and
includes some good reasons for why our numbers look as they do today. For exam-
ple, historians believe that between 970 and 1082, the numbers 2 and 3 changed
significantly, rotating 90 degrees from their original written position. This is
thought to be due to how scribes worked: Sitting cross-legged, they wrote on a
scroll they wound from right to left across their body. This caused them to write
from top to bottom, not our usual left to right; the script was then rotated when
the scroll was read.
How are numbers classified?
The set of natural numbers are also called integers—or counting or whole numbers—
which are usually defined as the positive and negative whole numbers, along with zero
(0). But many times mathematicians do not use the term “natural numbers,” and
instead define numbers based on the following terminology and/or symbols: 71
MATH BASICS
Different cultures generally employed one of two strategies when creating symbols for numbers: multiple marks
that indicated single numbers or multiples of fives or tens (e.g., Babylonian, Egyptian, Mayan), or a more
abstract system using a single symbol for the numbers one through nine, with numbers then being shifted over
one or more places to indicate multiples of ten, hundreds, etc. (e.g., Hindu, Hindu-Arabic).