Fractions and decimals trip up even confident writers. Is it "two-thirds" or "two thirds"? Do you write "0.5" as "zero point five" or "one-half"? Small choices like these change meaning, especially on cheques, invoices, and school assignments. Here is a clear set of rules you can use every time.

Fractions in words

Write simple fractions with a hyphen: one-half, two-thirds, three-quarters, five-eighths. The top number (numerator) is a cardinal number and the bottom number (denominator) is an ordinal number. So 3/4 becomes "three-quarters" and 7/10 becomes "seven-tenths". When a fraction is part of a sentence, the hyphen keeps it readable: "She ate two-thirds of the cake." Without the hyphen, the same words can read like a clumsy list of numbers.

Mixed numbers need "and"

A mixed number joins a whole number to a fraction with "and": 2 1/2 is "two and one-half", and 4 3/4 is "four and three-quarters". Never drop the "and" — "two one-half" reads like two separate quantities.…