Alberto is stacking firewood. He puts 20 logs on the bottom row. Then he stacks each row so that there is 1 fewer log than the row below. Which of the following can be used to determine the total number of logs in 10 rows?

The number of logs in each row decreases by 1: 20, 19, 18, and so on. Since the difference between consecutive terms is always −1, the row counts form an arithmetic series. Therefore, an arithmetic series can be used to find the total in 10 rows.

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