1
First, it's important to learn the spelling of small numbers,
since larger numbers are built upon those numbers.
The first twenty are:
one, two, three, four, five, six, seven, eight, nine, ten,
eleven, twelve, thirteen, fourteen, fifteen, sixteen, seventeen, eighteen, nineteen, and twenty.
Take careful note of four and eight, which are homonyms for other unrelated words.

2
Once we get past twenty, we must start using a hyphen.
For example, the number 23 is written twenty-three.
It's not a big deal, but the proper way to do this is using a hyphen as shown.
Another example would be 78 written as seventy-eight.

3
For numbers bigger than 100, we don't say the word "and."
Everybody does, including the famous Disney movie about the dogs, but it's not correct.
For example, the number 101 is written "one hundred one."
The number 736 is written "seven hundred thirty-six."
Notice there is no hyphen in between the number of hundreds and the word "hundred,"
but there is between the thirty and the six. Again, there is no "and."

4
The reason why we don't write or say "and" in those numbers
is because we use the word "and" to imply a decimal point.
For example, although we could say 7.2 as "seven point two,"
the proper way to say or write this number is "seven and two tenths."
We use the "and" to mean the decimal point.
Another example is 234.79, which we would write as
"two hundred thirty-four and seventy-nine hundredths."

5
Speaking of decimal points,
it's important to understand that place values to the right of a decimal point include the letters "th."
That is why we used the words "tenths" and "hundredths" above.

6
In order to properly write large and small numbers,
you must have an understanding of place value,
but that goes outside the scope of this article.
For example, you must learn to recognize 3,020,007 as "three million twenty thousand seven."
Similarly, you should learn to recognize 0.005 as "five thousandths."

7
Again, none of this is a big deal,
but knowing how to do this task properly will result in better test scores
especially in the lower grades where this is emphasized.
It will also allow you to write your numbers properly in formal writing.
See the Resource section below for more about this topic.

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 1    One
 2    Two
 3    Three
 4    Four
 5    Five
 6    Six   
 7    Seven
 8    Eight
 9    Nine
10    Ten
11    Eleven
12    Twelve
13    Thirteen
14    Fourteen
15    Fifteen
16    Sixteen
17    Seventeen
18    Eighteen
19    Nineteen
20    Twenty
21    Twenty-one
22    Twenty-two
30    Thirty
31    Thirty-one (37 thirty-seven)
40    Forty
50    Fifty
60    Sixty
70    Seventy
80    Eighty
90    Ninety (99 ninety-nine)
100   One hundred
101   One hundred one
499   Four hundred ninety-nine
748   Seven hundred forty-eight

1,000    One thousand
1,003    One thousand three
1,049    One thousand forty-nine

10,000    Ten thousand
11,000    Eleven thousand
25,608    Twenty-five thousand, six hundred eight

100,000    One hundred thousand

1,010,010    One million, ten thousand ten

1,000,000,024    One billion, twenty-four

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