为什么不是新的revenue直接乘以30%再乘以1+通胀率
问题如下图：
选项：
A. 
B. 
C. 
解释：
NO.PZ201512300100000604 ForecasteCOGS = Base COGS × COGS increase ForecasteCOGS = 30 × 1.0476 = 31.43
NO.PZ201512300100000604 老师这里的COGS为什么要这么计算，题目里面Archway’s cost of goo solw30% of sales.不是说COGS是sales的百分比，算出来sales直接乘以比例就可以了呀
NO.PZ201512300100000604 [（1-3%）*（1+5%）*sales - 30%*sales*(1+8%)*(1-3%) ] / （1+5%）*（1-3%）*sales，分子分母约去sales计算出答案69.14%，老师好 分母打亮部分这里 为什么不用再乘以（1+5%） 谢谢。
NO.PZ201512300100000604 老师 为什么计算COGS的时候不能从sales-base出发去推导 也就是为什么不是（1+5%）（1-3%）*30%（1+8%）？
67.0%. 69.1%. C is correct. The calculation of Archway’s gross profit margin for 2015, whireflects the instry-wi 8% inflation on cost of goo sol(COGS), is calculatefollows: Revenue growth = (1 + Priincrease for revenue) × (1 + Volume growth) - 1 Revenue growth = (1.05) × (0.97) - 1 = 1.85% COGS increase = (1 + Priincrease for COGS) × (1 + Volume growth) - 1 COGS increase = (1.08) × (0.97) - 1 = 4.76% Forecasterevenue = Base revenue × Revenue growth increase Forecasterevenue = 100 × 1.0185 = 101.85 ForecasteCOGS = Base COGS × COGS increase ForecasteCOGS = 30 × 1.0476 = 31.43 Forecastegross profit = Forecasterevenue - ForecasteCOGS Forecastegross profit = 101.85 - 31.43 = 70.42 Forecastegross profit margin = Forecastegross profit/Forecasterevenue Forecastegross profit margin = 70.42/101.85 = 69.14%老师，我刚才问的问题自己想通了，他计算COGS的时候，不是sales-based
