Question 853442
If the interest is simple interest (it never is on a credit card, it's compounded), then the 52-week rate is 11.96%.  Divide by 52 to get a single week's interest.
11.96/52 = 0.23 per week
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If you want to play with some real-life scenarios, you can use the calculators at http://www.1728.org/compint.htm
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If you actually borrow from a credit card company, most of them compound the interest daily.  So the first charge is charged interest on the purchase only.  The second day, however, the interest is charged on the purchase plus the interest from the first day.  And the third day, the interest is charged on the purchase plus the interest from the first and second days.  You can see how a small purchase can quickly become a large one due to interest.  Use your cards wisely, or not at all.