Why is this 18, when "naw" is 9? This looks so like 19 that I don't think I'm going to be able to remember it. Any help?
For ordinary counting the decimal system is universal by now, so once you know the first ten numbers you can construct the rest.
The vigesimal system with all its quaint peculiarities, especially from 15 to 19, is only used with expressing the date orally, the written expression of the date having been simplified.