When you use a credit card to buy something online, the credit card company charges a fee to
the store, which you often don't see because that fee is charged to the store without affecting
what you pay. You just bought something whose regular price including tax would have been
$50, but you used a coupon which reduced the amount by 20%. The credit card company
ended up charging $1 to the store as a fee. What percentage of the amount you paid the store
was that credit card fee?