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A retailer sell cameras at profit of 10% if he had paid 10% less for it and sold it for $10 more he would have made a profit of 25%.how much did it cost him and how much did he sell if for?
Note:i know to solve this problem using formula which in turn takes me 5 minutes to solve.
Please give me a solution for this problem to solve in a minute.

Assume a cost price and then work backwards.

Let us say the cost price of the camera is $100. Then his initial selling price is $110.

His new cost would be $90. He will make a profit of 25% as stated if he had sold it for 90 + 25% of 90 = 90 + 22.5 = 112.5

i.e., his new selling price is $2.5 more than the old SP.

However, the question states that the new SP is $10 more than the old SP. Therefore, your assumption of CP ($100) has to be revised by the same factor of 4. So, the CP should be $400.