What inventory method will generate the highest operating income? ABC co. has the following data for the month ended January 31, 2021. ABC uses periodic inventory system: Date Units Unit cost or selling price 1/1 Beginning Inventory 90 $30 1/8 Purchase 110 29 1/12 Sale 120 40 1/18 Purchase 100 28 1/20 Sale 80 45 1/24 Purchase 130 27 1/29 Sale 100 45