On July 15, 2021, the Nixon Car Company purchased 1,000 tires from the Harwell Company for $50 each. The terms of the sale were 2/10, n/30. Nixon uses a perpetual inventory system and the gross method of accounting for purchase discounts.

Required:
1. Prepare the journal entries to record the (a) purchase on July 15 and (b) payment on July 23, 2021.
2. Prepare the journal entry for the payment, assuming instead that it was made on August 15, 2021.
3. If Nixon instead uses a periodic inventory system, explain any changes to the journal entries created in requirements 1 and 2.