The price of a stock decreased by 60 cents one week, decreased 10 cents the next week, and decreased another 20 cents the following week. What is the average change in the price of the stock over the three weeks?

Treat each decrease as a negative change: −60, −10, and −20 cents. Their total change is −90 cents, and dividing by 3 weeks gives an average change of −30 cents per week. So the correct choice is negative 30 cents per week.

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