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Questions & Answers about Это три километра.
Why does the word for kilometres end in -а (километра) instead of a regular plural ending?
This is a special rule for Russian numbers. After the numbers 2, 3, and 4, you must use the genitive singular form of the noun, not the normal plural. Since километр is a masculine noun ending in a consonant, you add an -а to make it genitive singular.
Where is the word for "is" in this sentence?
In Russian, the present tense of the verb to be (am, is, are) is usually left out. You simply put the subject and the amount together. Literally, the sentence is just: That — three kilometres.
Shouldn't Это change to match the plural amount?
No. When you use Это to introduce something (meaning "this is", "that is", or "these are"), it stays in this default form. It does not change to match the gender or quantity of the words that come after it.
Does the number три change depending on the gender of the noun?
No, it stays the exact same! While the numbers 1 and 2 have different forms depending on whether the following noun is masculine, feminine, or neuter, the numbers 3 (три) and 4 (четыре) use the same form for all noun genders.