Solve please........

Harish Kumar (IPCC) (475 Points)

24 July 2012  

calculate the closing Stock on 31.03.2011

Particulars 31.03.2010      31.03.2011

Opening Stock  30,000        35,000

Purchases  3,25,000          4,20,000

Sales       4,00,000                   5,00,000

The profit margin remains unchanged a) Rs. 35,000 b) Rs. 50,000 c) Rs. 55,000 d) Rs. 60,000

answer is (c)Rs. 55,000

Please explain ....how is it....??