How to write numbers

In writing numerals may be spelled out or be represented by figures: Boing 567.

NOTE:

In writing, commas (but not full stops) are used to separate thousands: 100, 456; 1, 000, 000; 1, 908, 367, 849.

Numerals in figures or in letters?

Although there is no definite rule, there are some guidelines that should be followed.

Usually most writers spell out numbers under 100 (as one, two, the third, for seven years, forty-five years old) and use figures for 100 and over (286 buildings). But large numbers are spelled out: The house was sold for $1 million.

A number that starts a sentence should always be spelled out, even if it is over 100: Three thousand forty-four voters selected Teresa.

Whenever mentioning parts of a book (page numbers, sections, chapters, exercises), figures are used: The teacher assigned exercise 12 on page 235.

In special or technical texts cardinals and ordinals should always be indicated by figures.