When writing numbers in full, hyphenate all numbers between 21 and 99 (less those divisible by 10).|
(Be aware that some grammar purists will expect you not to write the word and when writing numbers in full – unless you mean point. For them, and denotes the decimal point. In other words, they will take seven hundred and twenty-four> as 700.24 not 724.)
Hyphens in NumbersRegardless of where they appear within the whole number, all numbers between 21 and 99 (except 30, 40, 50, 60, 70, 80, and 90) should be hyphenated. (There is no need to use commas.)
FORTY NOT FOURTY
The number 40 is spelt forty and not fourty.
Be aware that some grammar purists (particularly in America) state that and is only used when writing numbers to denote a decimal point.
In other words, if you wrote one hundred and one, they would take this to mean 100.1 and not 101.
POINT OF INTEREST – NO A BETWEEN 1 AND 999
Interestingly, if you adopt the rule above regarding and and start writing out all the numbers from 1 upwards, you will reach 1000 before you use the letter a.