Numbers ending in 1

Question

Quoting this article on Russian plurals:

If the number is 1, or the number ends in the word “один” (example: 1, 21, 61) (but not 11), then you should use the case (singular) that is suitable for the position in the sentence. The number one declines like an adjective.

What exactly does that mean? Are numbers ending with 1 used in singular ?

Edit: I would appreciate it if someone could provide some examples of those numbers in proper sentences.

Answer 1

The number 1 or the word "один" takes singular forms of nouns:

В комнате был только один человек. (There was only one person-SINGULAR in the room).

It is true for all numbers that end in "один" (the actual word you say, not the last digit, so it's different for 11 'одиннадцать'):

В июле 31 / тридцать один день. (July has 31 day-SINGULAR)

11 / одиннадцать does not end in "один", but rather in "-надцать". That's why a different rule applies to this number. It doesn't defy logic and takes plural noun forms.

Он спал 11 часов. (He slept for 11 hours-PLURAL+GENITIVE.)

The word "один" can be declined for gender and case (so it behaves similar to adjectives):

• одна девочка (one-FEMININE+NOMINATIVE girl)

• один мальчик (one-MASCULINE+NOMINATIVE boy)

• одно слово (one-NEUTER+NOMINATIVE word)

• Я знаю одну девочку (I know one-FEMININE+ACCUSATIVE girl+ACCUSATIVE)

• Я знаю одного мальчика (I know one-MASCULINE+ACCUSATIVE boy+ACCUSATIVE)

• Я знаю одно слово (I know one-NEUTER+ACCUSATIVE word+ACCUSATIVE) and so on.