inventories have a significant effect on profits. a business that makes or buys goods to sell must keep track of inventories of goods under all accounting and income tax rules. an example illustrates why. fred buys auto parts and resells them. in 2008, fred buys $100 worth of parts. he sells parts for $80 that he bought for $30, and has $70 worth of parts left. in 2009, he sells the remainder of the parts for $180. if he keeps track of inventory, his profit in 2008 is $50, and his profit in 2009 is $110, or $160 in total. if he deducted all the costs in 2008, he would have a loss of $20 in 2008 and a profit of $180 in 2009. the total is the same, but the timing is much different. most countries' accounting and income tax rules (if the country has an income tax) require the use of inventories for all businesses that regularly sell goods they have made or bought.