Mathematical fractions (две пятых)

Let's head out to the fields and learn the vocabulary for land surveying (межевание).

Mathematical Fractions

When measuring and dividing land, you will often express mathematical fractions like "two fifths" or "three sevenths."

In Russian, a fraction is conceptually a part of a "fraction" (дробь), which is a feminine noun. Even though this noun is usually omitted, it controls the grammar of the numbers used. To form a general mathematical fraction (where the numerator is greater than one):

  • Numerator (top number): Use a feminine cardinal number. For "two," you must use две. (Numbers like три and четыре do not change by gender in the nominative).
  • Denominator (bottom number): Use an ordinal number in the Genitive plural (e.g., пятых, седьмых, десятых).

Just like in English, the noun that follows the fraction (the thing being divided) takes the Genitive case to mean "of the...".

The surveyor went to measure out two fifths of a hectare.
Геодезист поехал отмерить две пятых гектара.

Notice how the numerator uses the feminine две, and the ordinal "fifth" (пятый) takes the Genitive plural form пятых.

The farmers sowed three tenths of the pasture for the sake of the harvest.
Фермеры засеяли три десятых пастбища ради урожая.

When a fraction acts as the subject of the sentence, the verb typically takes a plural form to agree with the plural quantity.