问题如下：
Steve notes that for the year just ended 2017, PZ’s cost of goods sold was 35% of sales. He assumes that all companies in the industry will experience an inflation rate of 5.5% on the cost of goods sold. Based on the summary of forecasts relating to PZ’s price and volume changes, PZ’s forecasted gross profit margin for 2018 is closest to:
选项：
A.65.17%.
B.44.30%.
C.52.89%.
解释：
A is correct.
考点：Income Statement Modeling: Operating Costs
解析：A是正确的。PZ 2018年毛利率的计算，计算方法如下:
销售额增长 = (1.06) × (0.98)-1 = 3.88%
COGS 增长率= (1.055) × (0.98) -1 = 3.39%
预测销售额 = 100 × 1.0388 = 103.88
预测 COGS = 35 × 1.0339 = 36.19
预测毛利润 = 103.88 - 36.19 = 67.69
预测毛利润率= 67.69/103.88 = 65.17%
我是按照老师讲课的思路来解的，先预测出2018年的sales, 然后COGS是2018年sales的35%再算上通胀，最后再算gross margin。
假设原来sales是1
预测sales=1.06*0.98=1.0388
预测COGS=0.35*1.0388*1.055=0.3835（销量减少已经考虑在sales的预测中了，不用再考虑）
gross profit margin=（1.0388—0.3835）/1.0388=63.08%
而答案的思路是在2017年的COGS基础上，算上通胀和销量的增长率，去预测2018年的COGS，这和老师讲的不太一样。老师是说先预测sales,然后根据COGS占sales的比例去预测COGS
