A simple rule for using numbers in writing is that small numbers ranging from one to ten (or one to nine, depending on the style guide) should generally be spelled out. Larger numbers (i.e., above ten) are written as numerals.
There are several rules of thought on how to handle writing numbers, but the most common is pretty simple. Spell out numbers under 10 (zero through nine), and use the numeric symbols for numbers 10 and up.
It is generally best to write out numbers from zero to one hundred in nontechnical writing. In scientific and technical writing, the prevailing style is to write out numbers under ten. While there are exceptions to these rules, your predominant concern should be expressing numbers consistently.
Spell out numbers under 10
When writing numbers under 10 in a sentence, they should be spelled out. This is true regardless of where they fall in a sentence. Mary read four new books last week and seven newspaper articles.
In general, words should be used for numbers from zero through nine, and numerals should be used from 10 onwards. This is true for both cardinal numbers (e.g., two, 11) and ordinal numbers (e.g., second, 11th).
The Chicago Manual of Style recommends spelling out the numbers zero through one hundred and using figures thereafter—except for whole numbers used in combination with hundred, thousand, hundred thousand, million, billion, and beyond (e.g., two hundred; twenty-eight thousand; three hundred thousand; one million).
Therefore, 11 in words = Eleven.
Numbers less than 10 are easy to read as words; Large numbers are difficult to read as words and easy to read as numerals. In general, conventions make life easier for writer and reader. There may be a slight disruption to the look of and reading of prose when interspersing numbers with words.
Numbers, dates and time are counted as words in writing. For example 30,000 = one word / 55 = one word / 9.30am = one word / 12.06.
Spell out numbers in dialogue unless they are excessively awkward. "You owe me one hundred and fifty-five dollars," he said is preferable to "You owe me $155," he said.
13 in words is written as “Thirteen”. 13 is 3 more than 10. In the number system, 13 is a number that represents a value or a count equivalent to it.
Generally, the trickiest numbers are those with FOUR, FIVE, EIGHT and NINE. Why? It's because some FOUR words are spelled with U, and others are not. Make an effort to learn FOUR, FOURTH and FOURTEEN with U.
Letters A, B, C and D do not appear anywhere in the spellings from 1 to 99 (one, two, … , ninety-nine), while letter D comes for the first time in 100 (hundred). Letters A, B and C do not appear anywhere in the spellings from 1 to 999, while letter A comes for the first time in 1000 (thousand).
This is (11) eleven, (12) twelve, (13) thirteen, (14) fourteen, (15) fifteen, (16) sixteen, (17) seventeen, (18) eighteen, (19) nineteen, and (20) twenty.
Option 'c' is Twelfth. It is the correct spelling of twelfth as there is a 'f' at the correct place and the vowel is also correctly placed.
Less Than Sign
An example for less than the inequality symbol is 5 < 10. It means that 5 is less than 10.
Ten is the base of the decimal numeral system, by far the most common system of denoting numbers in both spoken and written language. It is the first double-digit number. The reason for the choice of ten is assumed to be that humans have ten fingers (digits).
398.101 is read as a three hundred ninety eight, one hundred one.