I have recently started learning Japanese and am at the moment a bit confused about the way numbers are used or referred to in Japanese.
1. Sometimes, the number Kanji are used and sometimes Arabic numerals are used. Can they be used completely interchangeably in modern Japanese?
2. The Kanji 号, 番 and 第 all seem to mean "number". What is the difference?
3. About the "counter for X" Kanji. I understand that each (countable, quantifiable) Japanese noun word W has an assigned counter Kanji which needs to be used if you want to say "five W" or "the fifth W", for example. For example, 匹 is the assigned counter word for 猫. If you want to say "n cats", you use 猫<number n>匹 and if you want to say "the nth cat" you use 猫<number n>匹目. Exceptions seem to include words for time like 日 (day) and 時 (hour), but there at least for the "how many" part, 間 seems to play a similar role : 二日間 is "two days" (although 二日 also can mean "two days") while for the "the nth W" part, no counter word is used (二日 also can mean "the second day", 二月 the second month or February etc.).
Did I get anything wrong here? Are there other important exceptions? For example, 5号室 can mean "the fifth room" or "room number five", is this because there is no assigned counter Kanji for 室 or is this an exception?
Another example I came across is 三階 for "the third floor". Here, neither a counter Kanji is used nor the Kanji 号 as in 5号室.
Any help much appreciated.
1. Sometimes, the number Kanji are used and sometimes Arabic numerals are used. Can they be used completely interchangeably in modern Japanese?
2. The Kanji 号, 番 and 第 all seem to mean "number". What is the difference?
3. About the "counter for X" Kanji. I understand that each (countable, quantifiable) Japanese noun word W has an assigned counter Kanji which needs to be used if you want to say "five W" or "the fifth W", for example. For example, 匹 is the assigned counter word for 猫. If you want to say "n cats", you use 猫<number n>匹 and if you want to say "the nth cat" you use 猫<number n>匹目. Exceptions seem to include words for time like 日 (day) and 時 (hour), but there at least for the "how many" part, 間 seems to play a similar role : 二日間 is "two days" (although 二日 also can mean "two days") while for the "the nth W" part, no counter word is used (二日 also can mean "the second day", 二月 the second month or February etc.).
Did I get anything wrong here? Are there other important exceptions? For example, 5号室 can mean "the fifth room" or "room number five", is this because there is no assigned counter Kanji for 室 or is this an exception?
Another example I came across is 三階 for "the third floor". Here, neither a counter Kanji is used nor the Kanji 号 as in 5号室.
Any help much appreciated.