A chemical decays in such a way that the amount left at the end of each week is 20% less than the amount at the beginning of that same week. What percent of the original amount is left after two weeks?
- A40%
- B60%
- C64%
- D80%
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Correct answer: C
Let be the original amount of the chemical. It loses 20% after each week, which means 80% of the chemical remains at the end of each week. End of first week:
At the end of the second week, 80% of the amount left at the end of the first week remains. End of second week: