Adrian's credit card statement shows a balance of $500 for the first 15 days of the billing cycle. On the 16th day, Adrian made a payment of $200, reducing the balance for the remaining 15 days. What is Adrian's average daily balance?

The average daily balance is the total of each balance multiplied by the number of days it applied, divided by the 30-day billing cycle. For the first 15 days, the balance was $500; after the $200 payment, it was $300 for the next 15 days. So the average is (($500 × 15) + ($300 × 15)) ÷ 30 = $400. The correct choice is A, $400.

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