NO.PZ2016012101000140
问题如下：
Cinnamon Corp. started business in 2007 and uses the weighted average cost method. During 2007, it purchased 45,000 units of inventory at €10 each and sold 40,000 units for €20 each. In 2008, it purchased another 50,000 units at €11 each and sold 45,000 units for €22 each. Its 2008 cost of sales (€ thousands) was closest to:(assume the companies use a periodic inventory system)
选项：
A.€490.
B.€491.
C.€495.
解释：
B is correct.
Cinnamon uses the weighted average cost method, so in 2008, 5,000 units of inventory were 2007 units at €10 each and 50,000 were 2008 purchases at €11. The weighted average cost of inventory during 2008 was thus (5,000 ×10) + (50,000×11) = 50,000 + 550,000 =€600,000, and the weighted average cost was approximately €10.91 =€600,000/55,000. Cost of sales was €10.91×45,000, which is approximately €490,950.
解析：2007年买的存货没全卖掉，2008年年初库存还有5000件，每件单价10块，2008年又采购了50000件，每件11块，加起来总成本=50000+550000=600000，再除以总件数55000，加权平均成本=600000/55000=10.91，这是2008年每件存货的成本，问的是2008年的COGS，2008年卖掉了45000件，COGS=45000*10.91=490950，用thousand作单位就是491。
periodic inventory system的时间一般是多久呢
