I am stumped on what my adjusting entry should be for the period for a FIFO Periodic Inventory system.

Beginning Inventory $500
Net Purchases for Period $2020
Ending Inventory $770

Purchases for the Period were Debited at $2020


My book tells me that an adjusting entry should be made, but I don't know which accounts are debited and credited. Thanks so much for your help.

The adjusting entry will be for the difference between the Beginning Inventory + puchases and the Ending inventory.

This Entry is:
Debit Cost of Goods Sold
Credit Merchandise Inventory