Answer:
Dunne Co.
1. Determine the inventory on June 30 and the cost of goods sold for the three-month period, using the first-in, first-out method and the periodic inventory system:
a) Inventory, June 30  = $32,864 (26 x $1,264)
b) Cost of goods sold = Cost of goods available for sale - Ending Inventory = $310,776 ($343,640 - $32,864)
2. Determine the inventory on June 30 and the cost of goods sold for the three-month period, using the last-in, first-out method and the periodic inventory system:
a) Inventory, June 30 =  $ 
Beginning Inventory 25 units at $1,200 = $30,000
Purchase on April 8, 1 unit at $1,240              1,240
Total Ending Inventory                              $31,240
b)Cost of goods sold = Cost of goods available for sale - Ending Inventory
= $311,400 ($343,640 - $32,240)
3. Determine the inventory on June 30 and the cost of goods sold for the three-month period, using the weighted average cost method and the periodic inventory system. Note: Round the weighted average unit cost to the nearest dollar and final answers to the nearest dollar:
a) Inventory, June 30 = $32,489.60 (26 x $1,249.60) 
b) Cost of goods sold = $311,150.40 (249 x $1,249.60)  
4. Compare the gross profit and June 30 inventories using the following column headings. For those boxes in which you must enter subtracted or negative numbers use a minus sign. 
                                      FIFO                  LIFO         Weighted Average
Sales                            $525,250         $525,250         $525,250
Cost of goods sold         310,776              311,400              311,150
Gross profit                  $214,474           $213,850           $214,100
Inventory, June 30       $32,864             $31,240           $32,489.60
Explanation:
a) Purchases and Sales Data:
Date     Transaction     Number of Units    Per Unit       Total
                                        In        Out                                 Cost      Sales
Apr. 3    Inventory          25                       $1,200     $30,000
       8     Purchase          75                         1,240        93,000
      11     Sale                               40          2,000                          80,000
     30    Sale                               30          2,000                          60,000 
May 8   Purchase          60                       1,260         75,600 
      10   Sale                               50          2,000                         100,000
      19   Sale                               20          2,000                          40,000
     28   Purchase          80                       1,260       100,800 
June 5 Sale                              40          2,250                          90,000 
      16   Sale                              25          2,250                         56,250
      21   Purchase          35                      1,264        44,240 
     28   Sale                              44          2,250                         99,000
b) Goods Available     275                                 $343,640
Cost of goods sold    249                                                   $525,250
Ending Inventory         26
c) Average cost of goods = Cost of goods available for sale/Quantity of goods available for sale = $343,640/275 = $1,249.60
d) FIFO, LIFO, and Weighted Average Costing Method under the periodic inventory system assume that 1) FIFO, the goods bought first are sold first; 2) LIFO, the goods bought last are sold first; and 3) Weighted Average, the cost of goods is the weighted average, and lastly that it is only when physical count is taken of inventory that one can estimate its value.  Unlike the perpetual inventory system, the periodic must wait till the end of a financial period to value stock.  The results for ending inventory under the weighted average method, using the perpetual inventory system differs from the results under the same method, using the periodic inventory system.