### Feel Like a Number? Part 3. The Earth Day Edition

by Anne Breitenbach

Our Earth Day post continues our look at exceptions to the basic rule, outlined in 4.31, that numbers below 10 are set as words rather than numerals. We’ve looked at Parts a–c previously. Let’s continue with Parts d–e. These are clear enough that it’s hard to find much of a toehold for ambiguity.

Before looking at the rules, though, there's one change from earlier editions of the Publication Manual that we should note. The rule that specific numbers of subjects or participants in an experiment are set as figures has been dropped. Thus,

The four participants each planted one tree for every year he or she had been alive.

It is appropriate to set as figures

d. numbers that represent statistical or mathematical functions, fractional or decimal quantities, percentages, ratios, and percentiles and quartiles.

So examples (from http://www.planetpals.com/fastfacts.html) include the following:

It takes 9 times more energy to make new cans than to use recycled cans.

Only 6% of household waste can’t be recycled.

About .33 of all water use is for flushing toilets.

Earth is two-thirds water, but all the fresh water streams represent 100th of 1%.

NB: There is one exception that is relevant to the percentage portion of the rule. Rule 4.32 b states that one should use words to express common fractions; thus,

e. numbers that represent time, dates, ages, scores and points on a scale, exact sums of money, and numerals as numerals

Examples (from http://www.earthday.org/) include the following:

Join the climate rally at 11:00 a.m. on the National Mall.

The official observation will last for 8 hr.

. . . 6- and 7-year-olds from San Antonio, TX will have a trash-free day.

The official observation will last for about eight hours.

NB: Use words for approximations of numbers of days, months, and years. So if the time range isn’t precise, the example would be

Our series on numbers continues next week.

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