The title was "English question", not "logical question" or "IQ question". The questioner expects an answer based on formal English language, not how practical we use in daily life. Maybe many of us don't know the answer and tried to skip it away.
it was a real cash transation when i bought a piece of second hand furniture from someone from cl. obviously it wasn't $5 but he needed to break the $20 dollar bill to give me $15 change. i asked if he had any change. he asked me how much i need. i said i needed change for a 20. he looked confused and said to me, oh you need change for 15.... so then i got confused and wondered if i said it wrong or not. i'm asking this because that guy is a physician from ubc and he speaks better english than me. so i wondered if i've said it wrong. i'm asking this purly from an english/grammar point of view. nothing tricky.
but like most of you said i generally say do you have change for $20 as well. just wondering if i'm saying it right.
In your case, you should just hand him 20 bucks and wait for him to give you 15 without saying anything.
To me, if you say "do you have change for 20", I would think that you want to break it down to 2 10s.
Just like last night, I went to restaurant, let's say the bill was 60 something and I gave him 80 and one extra 20. I asked the waiter if I can have 2 10's from the 20.
I would not worry if he has change for 80. If he does not, he would tell me and ask to see if I have smaller bill.
If I were you, I will say "I only have a $20 bill. Is that okay?", or "Sorry, I don't have anything smaller". When you say "Do you have any change for $20", you are asking that person to break a $20 to spare changes or something smaller.
B仔 is right. It's about English usage in different places. Just like rubber/eraser, garbage bin/rubbish bin, flash light/torch
When you ask "do you have change for $15", he probably thought you want specific changes for the $15 (Let's say 1 $10, 1 loonie and 2 toonie). That's why he looked confused.
Like I said, for my previous cashier experience, no one asked me "do you have change for $20" unless they want to break the bill for bus or whatever. So I don't think it's the proper way to ask this question.