Given, marked price = 500

Discount given = 10%

So, selling price = 500 - 500*10%

                       = 500 - (500*10)/100

                       = 500 - (5*10)

                       = 500 - 50

                       = 450

Now, shopkeeper earns a profit of 25%

Let cost price is x

Now x + x*25% = 450

=> x + 25x/100 = 450

=> x + x/4 = 450

=> (4x + x)/4 = 450

=> 5x/4 = 450

=> 5x = 450*4

=> x = (450*4)/5

=> x = 90*4

=> x = 360

So, the actual cost of the article is Rs. 360