単数、複数

please refer to the definition of the word 'number' on the weblio dictionary.
refer to the definition of noun 1-b.
名詞
1
b不可算名詞 [しばしば the number] 〔人・ものの〕総数; 人数，個数 〔of〕.
The number of students has been increasing. 学生数は増加してきている 《★【用法】 単数扱い》.

:number on the weblio.
https://ejje.weblio.jp/content/number
:example video.
https://youtu.be/qBMTtI8Z6CE?t=261