Why is the letter o used when the correct word should be zero? [ as in a number?

Answer 1

dnldslk's first two reasons pretty much explain it. Remember, this is colloquial speech. The point is not "getting it precisely right" as in communicating easily. So long as it is clear in the context that you mean to communicate a NUMERAL -- say you're telling someone a set of phone numbers-- they should have no difficulty in understanding you... and it's a lot quicker.

Actually, if you look at a few dictionaries, you'll find this use acknowledged. For example:

2. the Arabic cipher; zero.

http://dictionary.reference.com/browse/O
(third entry on the page, listing uses of "O" as a symbol)

Answer 2

1. They look the same.
2. It’s faster to use a one syllable word than a two.
3. People like to fool around with language. It’s more fun that way.
4. People like to introduce a little weirdness to a rigid subject like math

Answer 3

It should not be. That's why we have zeros and o's to distinguish the two.

You would not write there are n0 o's in the number 5.

You would write there are no 0's in the number 5.