For those talking about interest.
Interest = Making money on money ... charging someone more money than you actually lend. Interest is earned and given on MONEY!
What you are doing here is a purchase of something at a higher cost, and paying it in installments. The higher cost is because of the easier payment terms. Instead of upfront, you pay monthly.
Simply ... purchase an X360 upfront you pay 21,250 ... purchase X360 in installements and you get it for (example) 25000 ... paying 10,000Rs upfront and 5,000 in 3 month installments. Or if you are going to go for 6 months ... 2500Rs installments. Its simple really! THere is no issue of interest here. You are not paying an extra amount just because you've borrowed some money, you are PAYING for something you've BOUGHT!