Case in compound numerals

Declining compound numerals is a complex task. To become proficient in this, follow these rules:

• Nominative and Accusative Government: In the Nominative case (and Accusative for inanimate objects), the final word of the compound numeral determines the case of the noun. If the numeral ends in 1 (except 11), the noun is in the Nominative Singular (e.g., 'двадцать один рубль'). If it ends in 2, 3, or 4 (except 12, 13, and 14), it governs the Genitive Singular (e.g., 'двадцать два рубля'). If it ends in 5–9, 0, or 11–14, it governs the Genitive Plural (e.g., 'двадцать пять рублей', 'сто двенадцать рублей').
• Cardinals vs. Ordinals: In cardinal compound numerals, every word changes (e.g., '155' in the Dative is 'ста пятидесяти пяти' - one hundred fifty-five). However, in compound ordinal numerals, only the final word declines (e.g., 'в сто пятьдесят пятом году' - in the one hundred fifty-fifth year).
• Large Numbers (1,000+): Words like 'миллион' (million) and 'миллиард' (billion) function as nouns and always govern the Genitive case of the following noun in all cases (e.g., 'с пятью миллионами рублей' - with five million rubles, or 'миллион населения' - a million of the population). Case agreement generally happens when the final word of the compound numeral is a regular number (e.g., 'с тысячей пятью рублями' - with one thousand five rubles). Note that 'тысяча' is unique in the Instrumental case: the noun-like ending '-ей' ('тысячей') governs the Genitive Plural ('с тысячей рублей' - with a thousand rubles), while the numeral-like ending '-ью' ('тысячью') triggers case agreement ('с тысячью рублями' - with a thousand rubles). However, 'тысячью' cannot be used with modifiers; if there is an adjective or pronoun modifying the thousand, the noun form 'тысячей' must be used, governing the Genitive Plural (e.g., 'с каждой тысячей рублей' - with every thousand rubles). Additionally, when used metaphorically to mean an indefinitely large amount, 'тысячью' still governs the Genitive (e.g., 'человек с тысячью лиц' - a person with a thousand faces).
• Case Agreement: For numbers below 1,000, once the numeral leaves the Nominative/Accusative, the noun usually agrees with the numeral's case (e.g., 'с пятьюдесятью рублями' - with fifty rubles).
• The '1' Exception and Pluralia Tantum: If a compound numeral ends in 'один' (one), the noun remains in the Singular but must match the case of the numeral (e.g., 'о двадцати одном студенте' - about twenty-one students). The exception is pluralia tantum nouns (words that only exist in the plural, like 'сутки' - days), which take the plural form 'одни' and keep the noun in the Plural (e.g., 'двадцать одни сутки' - twenty-one days). However, while collective numerals are used for single digits (e.g., 'двое суток'), you cannot use them in compound numerals ending in 2, 3, or 4 (e.g., 22, 23, 24). Instead, you must rephrase the noun entirely (e.g., use 'двадцать два дня' instead of trying to combine 22 with 'сутки').
• Gender Agreement for 1 and 2: The numbers 1 and 2 must agree in gender with the noun even when they are at the end of a compound numeral (e.g., 'сорок две машины' - forty-two cars). Additionally, 1 and 2 must agree in gender with 'noun-like' numbers inside the compound numeral itself (e.g., 'две тысячи' - two thousand since 'тысяча' is feminine, but 'два миллиона' - two million since 'миллион' is masculine).
• Animacy Rule: If a compound numeral ends in 2, 3, or 4, the Accusative case is always identical to the Nominative, even for animate objects (e.g., 'встретил тридцать три человека' - met thirty-three people). This is a crucial difference from simple numbers 2, 3, and 4, which DO observe the animacy rule (e.g., 'встретил трех человек' - met three people). Compound numerals ending in 1, however, fully agree in gender, case, and animacy with the noun in the Accusative case (e.g., 'вижу двадцать одного студента' - I see twenty-one students, 'вижу двадцать одну машину' - I see twenty-one cars). Note that for all numbers ending in 5–9, 0, and 11–14, the Accusative is also identical to the Nominative, and the noun simply takes the Genitive Plural (e.g., 'вижу двадцать пять студентов' - I see twenty-five students).
• Specific Word Patterns:
  - 40, 90, 100: Only have two forms: Nom/Acc vs. everything else ending in -а.
  - 50-80 and 200-900: Both roots within the word decline (e.g., 'пятьдесят' becomes 'пятидесяти' in the Dative, and 'пятьюдесятью' in the Instrumental; 'триста' becomes 'тремястами' in the Instrumental).