



 
Hi Christine, If a quantity changes over time the term "percentage change" usually refers to the change, as a percentage of the quantity at the earlier date, where the change is the later quantity minus the earlier quantity. In your case the quantity at the earlier date is 2009 so the earlier quantity is 100, and the change is $104  100 = 4.$ Hence the percentage change is \[\frac{4}{100} \times 100 = 4\%\] Penny  


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