How are we supose to know this with just the pronunciation ? Its kind of confusing that we know 20's and not sure wish one its 1 ! ??
It is done like this so that sometimess you make a mistake, then you will learn from your mistake and remember.
1-10: yi er san si wu liu chi ba jiu shi. bai means hundred. er shi = 20 (2 tens), wu shi = 50 (5 tens) yi bai = one hundred, si bai = four hundred, etc.
I just think we were supposed to have the translation a little bit more specified