# Thread: What branch of mathematics studies the types of numbers? (Cardinal, Ordinal, Nominal)

1. ## What branch of mathematics studies the types of numbers? (Cardinal, Ordinal, Nominal)

I ask this question in context of a question about the date. For example, what is today's date if today is Wednesday and last Sunday was the 20th (of January)? Rephrased, the equivalent question is: What is today's date if today is FOUR and last ZERO was the 20th. Four and Zero are used as cardinal numbers.

2. ## Re: What branch of mathematics studies the types of numbers? (Cardinal, Ordinal, Nomi

Cardinal numbers is referenced to cardinality, from what I remember. We talked about that kind of topics in discrete mathematics, so I would try there first. Either that or a number theory book.

Ordinal numbers deal with sets if I remember correctly, so again try discrete or number theory.

Nominal numbers to me are just index numbers, you index with them....might check computer programing books if you want to do something fun with indexes.

Hope that helps.

Cheers,
Obitus

3. ## Re: What branch of mathematics studies the types of numbers? (Cardinal, Ordinal, Nomi

Originally Posted by Elusive1324
I ask this question in context of a question about the date. For example, what is today's date if today is Wednesday and last Sunday was the 20th (of January)? Rephrased, the equivalent question is: What is today's date if today is FOUR and last ZERO was the 20th. Four and Zero are used as cardinal numbers.
Why is it that the day of the week is a cardinal number, but the day of the month (20th) is an ordinal number?

4. ## Re: What branch of mathematics studies the types of numbers? (Cardinal, Ordinal, Nomi

Originally Posted by emakarov
Why is it that the day of the week is a cardinal number, but the day of the month (20th) is an ordinal number?
To be honest, I don't remember why I thought that was the case... I think I reasoned that the days of the week are cardinal because cardinal numbers are used in "naming" and so any mathematical operations on them would be meaningless (in the same way that it doesn't make sense to subject Sunday from Wednesday). In contrast, I think I reasoned that days of the month were ordinal numbers, which are used to identify "rank"/position because subtracting one calender day of the month from another would have meaning (17th of May - 13th of May = 4 days of May (17 to 16, 16-15, 15-14, 14-13 days))