I know, I suck at percentages, but I'm trading in a few games at GameStop tomorrow so I can get Batman: Arkham City and they have a deal where if you trade in your old games you get a 30% bonus extra store credit. The regular credit comes to around $25 if you didn't get the 30% bonus, so I'm just trying to see how much I would with the extra credit added. Thanks.

$25 * 30%
25*3
75
now move the decimal one place
7.5
$7.50
$32.50 with the 30%
25*3
75
now move the decimal one place
7.5
$7.50
$32.50 with the 30%

7.50 dollars

You would take .30 x 25 which equals $7.50.