Post Office Confusion

So, I ran to the post office today to pick up the stamps for my Christmas cards. I was 3rd in line. The girl that was at the window was having a hard time...

Girl: 'I need 5 rolls of stamps, please.'

Postal Worker: 'How many individual stamps do you need?'

G; '5 rolls.'

PW: Yes, Ma'am. 5 rolls of 100 stamps each?'

G: 'I guess. Is that what a normal roll is?'

PW: 'Yes.'

G: 'Then that's what I need.'

PW: 'Well, I am out of the regular rolls, but I have rolls with 50 stamps in them so I will give you 10 of those.'

G: 'But I only need 5 rolls.'

PW: 'Yes, but 5 regular rolls is 500 stamps. If these only have 50 stamps per roll, you will need 10 rolls to get the same number of stamps.'

G: 'Oh, ok.'

PW rings up 10 rolls and give total.

G: 'So, I got 10 rolls and that is the same as 5 normal rolls?'

PW: 'Yes.'

G: 'OK. Just checking.'

G pays and leaves.

WOW!