Learn English – Singular or plural form of “digit” when referring to digits of individual numbers

It has less to do with the actual number, and more to do with how the number is said or written.

Singular nouns:

Any time the number is "one", or a fraction with "one" in the numerator, the result is singular. This also applies to negatives. See Is -1 followed by a singular or plural noun?

• One apple
• 1 apple ("one apple")
• Half an apple
• One half of an apple
• 1/2 apple ("one half apple" or "half of an apple")
• 1/4 apple ("one quarter apple" or "one quarter of an apple" or "one fourth of an apple")
• -1 volt ("minus one volt", "negative one volt")

Plural nouns:

Any decimal number, including 1.0, is plural. See Should we use plural or singular for a fraction of a mile?

• 1.0 apples ("one point zero apples", "one point oh apples")
• 0.5 apples ("zero point five apples", "oh point five apples")

Complicated cases:

Fractions with numerators larger than one can be handled both ways. This also applies to percentages. The plural form is used for countable objects, and the singular form is used for non-countable objects. See Is two-thirds plural?

• 2/3 of the people are here. (We are counting people.)
• 2/3 of the soda was left over. (We are not counting soda.)
• 75% of the computers are broken. (countable)
• 75% of the rice was eaten. (not countable)

Complex and imaginary numbers:

Complex and imaginary numbers only appear in technical contexts. I can only think of examples with units, for example:

• 5.7+3.1j kΩ at 500 Hz
• -1.0+0.9j mV at 10 kHz

Note that engineers usually use "j" instead of "i" to avoid confusion with I, the symbol for current. Mathematicians use "i".

In technical contexts, quantities for should be written with numerals and units should be written with abbreviations, which do not take plural. So "5 V" is okay, but "five volts" is only okay in non-technical contexts.

You can absolutely pluralize surnames without making them possessive. Apostrophes aren't needed in pluralization without possession. When you pluralize a name, you are pluralizing a noun. Most of the time, rules for pluralizing common nouns work the same way for proper nouns. (Add an -s or -es as is appropriate.) Example 1: There are four people in the Smith family. Together, they are the Smiths. Example 2: There are four people in the Jones family. Together, they are the Joneses.

If a name ends in a vowel, the rules can be a little bit different than with common nouns. Just remember that you should never change someone's name. You add to it to pluralize it, but the root (the name) remains unchanged. (Don't change -y to -ies, etc.) Example 1: The Rosetti family becomes the Rosettis. Example 2: The Murphy family becomes the Murphys.