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### Whole Numbers and Place Values

Objective: Introduce the set of whole numbers and place values.

We begin by defining a set as a collection of objects, typically grouped within braces { }, where each object is called an element.  For example, a set of colors, named C, is expressed as follows:
$C = \left\{ {{\rm{red, green, blue}}} \right\}$
When studying mathematics, we focus on special sets of numbers.  The set of natural numbers, or counting numbers, is an infinite set that is denoted using $$\mathbb{N}$$.
$\mathbb{N} = \left\{ {1,\,2,\,3,\,4,\,5,...\} } \right.{\rm{ Natural Numbers}}$
The three periods (…) is called the ellipsis mark and indicates that the numbers continue without bound.  We define the set of whole numbers, denoted using $$W$$, to be the set of natural numbers combined with zero.
$W = \left\{ {0,1,2,3,4,5,...\} } \right.{\rm{ Whole Numbers}}$
Developed between the 1st and 5th centuries, the Hindu-Arabic numeral system is the most common positional numeral system. This system allows us to express any whole number using the following set of ten digits.
$digits = \left\{ {0,1,2,3,4,5,6,7,8,9} \right\}$
A whole number is expressed using these digits and place values according to the following illustration.
For example, the average distance from the Earth to the Moon is 238,857 miles.
A number is written in expanded form to show the value of each digit. Here is the number 238,857 written in expanded form:
$200,000 + 30,000 + 8,000 + 800 + 50 + 7$
Example: Write in expanded form:
a. 375              b. 61,532         c. 5,102,700
a. $$375 = 300 + 70 + 5$$
b.$$61,532 = 60,000 + 1,000 + 500 + 30 + 2$$
c. $$5,102,700 = 5,000,000 + 100,000 + 2,000 + 700$$

Try this! Write in expanded form:
a. 8,014,050                b. 71,324                     c. 68,090,004
a. $$8,000,000 + 10,000 + 4,000 + 50$$
b.$$70,000 + 1,000 + 300 + 20 + 4$$
c. $$60,000,000 + 8,000,000 + 90,000 + 4$$

Digits are grouped in sets of three, called periods, separated by a comma.   It is sometimes acceptable to leave off the comma. For example, the four digit number 1,561 can also be written as 1561.  From the right, each set of three digits represents the number of ones, thousands, millions, billions, and so on.
A number is read by starting with the leftmost period. With the exception of the ones period, the name of the period is added after verbalizing the corresponding number. For example, 238,857 miles is read, “two hundred thirty-eight thousand, eight hundred fifty-seven miles.” Note that the comma in the written sentence matches the comma in the number.

Example: In 2012, the world population was approximated to be 6,176,534,320 people. Write this number in words.

Solution: Begin by identifying the value of each period.  Use this value for each three digit numerical grouping.

Note: Do not use the word “and” when writing whole numbers in words. As we will see, this word is reserved for the decimal.
Answer: Six billion, one hundred seventy-six million, five hundred thirty-four thousand, three hundred twenty people.

Example: Write the following numbers using words.
a. 371                          b. 71,051                     c. 67,151,205