Writing and Saying Numbers

Numbers Over 20

Are written with a hyphen: Ex: 27 (twenty - seven); 54 (fifty - four).
When writing a cheque we often use words for the pounds or dollars and figures for the pence or cents. Ex: $99.99 (ninety - nine dollars and ninety nice).

Numbers Over 100

Ex: 123 (one hundred and twenty three). The "and" is pronounced /n/ and the stress is on the final numbers. In American English the "and" is sometimes left out.

Numbers Over 1,000

Ex: 1200 (one thousand two hundred/ twelve hundred); 1345 (one thousand three hundred and forty five).
There is Informal forms are most common for whole hundreds between 1100 and 1900. A comma or a space or often used to divide large numbers into groups of 3 figures. Ex: 56,789 or 56 789 (fifty six thousands seven hundred and eighty nine).

Fractions

Ex: 1/2 (a/ one half); 1/4 (one fourth/ a quarter); 2/3 (two thirds); 3/9 (three ninths)...
For emphasis use "one" instead of "a"
More complex fractions:
Use "over". Ex: 24/78 (twenty - four over seventy - eight); 57/456 (fifty - seven over four five six).
Whole numbers and fractions:
Use "and". Ex: 3 1/2 (three and a half).