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A company sells 10,000 skateboards a year at $66 each. All sales are on credit, with terms of 3/10, net 30, that is, a 3% discount if payment is made within 10 days; otherwise full payment is due at the end of 30 days. One half of the customers are expected to take advantage of the discount and pay on day 10. The other half are expected to pay on day 30. Sales are expected to be uniform throughout the year for both types of customers. What is the expected average collection period for the company?