Why do we include the difference between opening and closing?
The expenses representing the purchases is accounted during the account period. The difference between the opening stock and the closing stock also should be reckoned along with the purchase made and the total sales made so that the correct profit can be arrived. For example the opening stock is Rs. 200. The purchase is Rs. 1000. Sales is Rs 1300 and the closing stock is Rs. 100. The profit is Rs. 300 without reckoning the stock The profit is Rs. 200 considering the stock position. Actually the cost of goods sold is 1100 that is apart from purchase 100 worth of goods from the opening stock is sold.