A conservationist determines that a particular beach is eroding at a rate of 1.1% each year. When writing an explicit formula to represent the amount of beach remaining each year, which value should she use as the common ratio?

A 1.1% yearly erosion means the beach loses 0.011 of its amount each year. The fraction remaining is 1 − 0.011 = 0.989, so the common ratio is 0.989. Choice C is correct; 1.011 would represent yearly growth instead.

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