How many times would you have to copy the bill before it became invisible? 
If you wanted to expand this bill back up to normal size with exactly one copy, what percentage would Dan have to set on the copier? 
You could turn a US dollar coin (26.5 mm diameter) into the size of a dime (17.91 mm diameter) by copying it four times at 90%. Give two other ways you could do the exact same thing. 