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State fractions in text in the simplest possible way, usually in words or decimals.  Do not combine a figure and a spelled-out number.

Generally spell out half, third, quarter:
            a half or one-half
            two and a half

Spell out simple fractions unless used in pairs or in dimensions, or fractions that are cumbersome:

3½ by 4½ feet

1/7000 (do not use th) of a pound
a hundredth or one-hundredth
thirty-nine millionths of an inch
Do not use commas in any part of a fraction with fewer than five digits.

Connect numerator and denominator with a hyphen unless either already contains a hyphen:
            one thirty-second
            forty-five hundredths
            twenty-one thirty-sixths

Note the difference:
            three-hundred thousandths (300/1000) and
three hundred-thousandths (3/100,000).

A fraction may be singular or plural depending on the intention of the writer.  Generally the object of the preposition of following the fraction governs the verb:
            Two-thirds of Nepal's population lives in these heavily farmed valleys; two-thirds of them live here.

Use figures for all numbers that contain decimals:
            3.4 inches of rain
            22.25 inches of snow
            a 12.5-billion-dollar deficit

If the amount is less than one, the unit of measurement is singular:
            .33 inch (not inches) a day.

If the figure is a one-digit decimal, use a zero before the point:
            0.3 inch a day