Section I. Basic Arithmetic
a. Whole Numbers. The number zero and the counting numbers (0, 1, 2, 3, 4,
5, 6, 7, 8, 9, 10, 11, 12, 13, 14, ...) are whole numbers. The first 10 whole numbers (0
through 9) are called digits.
b. Powers of Ten. Our number system is based upon the powers of ten. That
is, the digit place to the immediate left of a given digit is worth ten times as much as the
given digit place, and the digit place to the immediate right is worth one-tenth as much.
For example, in the number 321, the one tells you how many ones (or units) are in the
number, the two tells how many tens, and the three tells how many hundreds. See
Figure 1-1. The number system.
a. The numbers to be added are the addends. The answer to an addition
problem is the sum. When you are doing a problem in addition, work from right to left.
Be sure to keep the columns of numbers in straight lines.
b. When you "carry" a number over to the next column to the left, you can jot it
down at the top of the column.