Tandem Supplies, an office supply store, uses a perpetual inventory system. Tandem recorded the following activity in the paper inventory account. COGS Date October 1 Activity Beginning Inventory Units 2,500 Cost Per Unit $16 Inventory 2,500 October 10 Purchase 5,100 $17 7,600 October 11 Sale 5,900 October 20 Purchase 4,800 $18 October 25 Sales 5,300