Approximate numerals by inversion

Approximative inversion is a common feature of colloquial Russian. While you can use words like примерно (approximately), inversion sounds more native and informal.

1. Word Order and Case Relationship
The case relationship between the numeral and the noun remains exactly the same as it would in a standard sentence. For example:

• Standard: пять минут (five minutes).
• Inverted: минут пять (about five minutes).
• Standard: два часа (two hours).
• Inverted: часа два (about two hours).

2. Preposition Placement
When a preposition is involved, it is typically 'wedged' between the noun and the numeral. This wedging is almost exclusively a feature of short, primary prepositions:

• Short prepositions (в, на, к, с): часов в шесть (at about six o'clock).
• The prepositions за and под: These prepositions inherently mean 'over/more than' and 'approaching/just under', especially for age and quantity. Inversion is the natural word order when combining nouns with these specific prepositional phrases: лет за сорок (over forty years old), градусов под тридцать (approaching thirty degrees).
• The preposition через: минут через десять (in about ten minutes).
• Derivative prepositions: The vast majority of derivative prepositions (like в течение, вместо, согласно) cannot be used in this inverted structure. Furthermore, using the preposition около (around/about) with inversion (e.g., около часов пяти) creates a semantic redundancy (pleonasm) and should be avoided. Use either the preposition (около пяти часов) OR inversion (часов пять), but not both.

3. Usage Restrictions and Nuances

• Verb Agreement: When an inverted approximative phrase acts as the subject of a sentence, both singular (neuter in the past tense) and plural verb agreements are standard. While singular is common (e.g., Человек десять стояло в стороне), plural agreement is fully standard in literary Russian and very common for animate subjects (e.g., Пришли человек десять).
• Case Flexibility: While most common in the Nominative and Accusative, this pattern can occur in oblique cases (e.g., Dative: часам к пяти). However, approximative inversion is generally unacceptable in oblique cases without a wedged preposition (e.g., you cannot say студентами пятью or часам пяти). The exception is the Genitive case, which is frequently used without a preposition to express approximate age, weight, length, or price (e.g., мальчик лет десяти, весом тонн пять). Note a special approximative construction with the preposition с and the Accusative case: рублей с пятьдесят (about fifty rubles).
• Time vs. Duration Ambiguity: Without a preposition, a phrase like часов пять can mean either 'about five hours' (duration) or 'about five o'clock' (specific time), depending entirely on context.
• The 'One' Exception: The numeral один (one) cannot be inverted to mean 'about one'. Instead, use около часа or the phrase час-другой.
• Fractions: This pattern is highly common with полтора and полторы (1.5), such as года полтора (about a year and a half) or часа полтора (about an hour and a half).
• Animate Groups: When referring to groups of people, the genitive plural form человек is used and inverted, not людей (e.g., you must say человек десять, never людей десять). This applies even if a more specific noun follows (e.g., человек пять инженеров rather than инженеров пять).
• Adjectives: If a noun is modified by an adjective, the adjective stays in front of the noun, and the numeral is placed after the entire noun phrase (e.g., долгих лет пять for 'about five long years').
• Compound Numerals: When the numeral consists of multiple words, the noun must precede the entire numeral phrase (e.g., рублей сто пятьдесят, not сто рублей пятьдесят).
• Round Numbers: This pattern works best with 'round' numbers (5, 10, 20, 50, 100). It is rarely used with specific compound numbers like 23 or 47.
• Compound Numbers Ending in 1: Compound numbers ending in 1 (21, 31, etc.) cannot undergo inversion.
• Noun-like Numerals: Words like тысяча, миллион, and миллиард generally do not participate in approximative inversion.