|Generally spell out one through nine and use figures thereafter:
six parts steam, 11 parts sweat
two to one against
42 to 36 in favor
Odds and ratios can be written in all numerals, especially when the numeral 1 is used:
10-to-1 return on investment
Spell out figures of speech such as fifty-fifty, unless the context makes numerals appropriate:
Others thought he had a 1-in-10 chance of winning, though he considered his odds were 50-50.