Writing Tip

Follow Common Practices in the Mechanics of Fractions

Difficulty Level: Basic

Recommendation: Follow common practices in the mechanics of fractions.

Fractions come in many varieties, but for this tip, I want to talk about three: decimal fractions, vulgar fractions (also called simple or common fractions), and percentages. Here are three ways to express the same quantity:

Decimal: 0.5
Vulgar: 1/2
Percentage: 50%

The denominator of a decimal fraction is always a power of ten: 1, 10, 100, 1000, and so on. They are very handy for expressing relationships that don’t translate nicely to a simple fraction or a percentage. For example, if you have a board that is 23 inches wide and 13 inches tall, the height-to-width vulgar fraction is 13/23. It may be easier to express this in decimal form (0.5652), which is easier to store and recall in your calculator.

When vulgar fractions are spelled out, hyphenate the numerator and denominator, as in “one-third of a banana.” Spell out vulgar fractions when they modify an adjective or noun (like “two-thirds finished” or “one-half speed”).

International Considerations

Punctuating numbers, including fractions, is not straightforward when you are communicating to an international audience. For example, in America, we use commas to separate “thousands,” as in 1,000 or 1,000,000. But in other countries, spaces or periods are used to segment whole numbers, such as 25 000 000 or 25.000.000. In English-speaking, some Latin American and many Asian countries, a period (.) or raised period (•) is used as the decimal separator; in many other countries, particularly in Europe, a comma is used (as in 25,46 versus 25.46).

Leading and Trailing Zeros

A leading zero before a decimal fraction is required (0.5 versus .5). However, trailing zeros are not necessary, although in science, engineering, and statistics, they can be retained to indicate a required precision or to show a level of confidence in the accuracy of the number: Although 0.080 and 0.08 are numerically equal, in engineering 0.080 suggests a measurement with more precision (less error) than 0.08.

Sound

Mixed numbers like 2 3/4 can also be spelled out, but in a scientific context, why not just say “2.75”? Sometimes, it might “sound” better to spell out vulgar fractions than use decimal fractions. This idea of “sounding” ties to your language instinct—the instinct to speak the words we read. Consider another example: “He ate 0.75 pies.” This sounds awkward, clumsy. Not so mellifluous. The reader is compelled by his pink language box to pronounce it. If you spell it out for the reader, you satisfy that strong urge to articulate: “He ate three-quarters of the pie” or “he ate three-fourths of the pie.” If you use 3/4, then a translation must take place between the pink math box and the pink language box.

Percentage

In “scientific copy,” such as technical reports, using the percent sign is perfectly appropriate. In “humanistic copy,” such as articles, fact sheets, and marketing collateral, spelling out “percent” is more appropriate than using the sign. The value and the word “percent” are not hyphenated, as in “10 percent increase.”