A trader buys goods at 20% discount on marked price. If he wants to make a profit of 25% after allowing a discount of 20%, by what percent should his marked price be greater than the original marked price ?

Let original M.P. = $$100x$$

Discounted amount = $$\frac{20}{100} * 100x = 20x$$

=> Amount at which trader buys = $$100x-20x$$

=> C.P. = $$80x$$

Profit amount = $$\frac{25}{100} * 80x = 20x$$

=> Amount at which trader should sell = $$20x+80x$$

=> S.P. = $$100x$$

Let the price at which he marked his price = $$y$$

=> $$\frac{y-100x}{y}$$ * 100 = 20

=> $$4y = 500x$$ => $$y = 125x$$

Now, % by which he should mark up his price more than the original marked price = $$\frac{125x-100x}{100x}$$ * 100

= 25%