AoPS Wiki talk:Problem of the Day/June 26, 2011

Solutions

Let equal the cost of the calculator before sales tax (the "base price"). The amount of sales tax can be represented as since it is given as percent. We know that the final price of the calculator, which is equal to the sum of the base price of the calculator and the amount of sales tax, is . Thus, , or . Dividing both sides by , we get .