A trader buys an article at 80% of its marked price and sells it at 10% discount on its marked price. His percentage profit is:

$12\frac{1}{2}$

Let the marked price = 100

then, the cost price = 80% of the marked price = 80

Discount offered on marked price = 10%

Then the selling price = 90% of the marked price = 90% × 100 = 90

Profit = 90 - 80 = 10

Profit % = \(\frac{10 × 100}{80}\) = $12\frac{1}{2}$