I am doing an analysis of Cost/Sales % (C/S%). At the same time, Ineed to compare it with previous month's C/S%. Below is my case.Say, Jan'12 C/S% = 13.1%, Feb'12 C/S% = 15.8% (Increase by 2.7%...

I am doing an analysis of Cost/Sales % (C/S%). At the same time, I need to compare it with previous month's C/S%. Below is my case. Say, Jan'12 C/S% = 13.1%, Feb'12 C/S% = 15.8% (Increase by 2.7% - 15.8% minus 13.1%) Jan'12 Sales = $8,465,000, Cost = $1,112,099 Feb'12 Sales = $865,156, Cost = $136,786 Further to that, I am required to work out the reason for the change, and the movement analysis of Sales and Cost have been performed. The movement as follows: 1) Selling Price Decreased by $2,844 2) Cost Increased by $937 3) Change in Sales Mix - Sales reduced by $7,597,000 and Cost reduced by $1,010,000 4) Change in Cost Absorption difference - Cost increased by $33,750 How do I determined the C/S% walk for each contributing reasons above, which ultimately equals to 2.7%? I have been working on this for quite sometimes but to no avail. Thank you in advance for your help.