A trader sells his goods at a discount 20%. He still makes a profit of 25%. If he sells the goods at the marked price only, his profit will be:

Let the marked price = Rs. 100
Then, SP = 100 - 20% of 100 = Rs. 80
Profit = 25%
Let His CP = X
SP = 80
X + 25% of X = 80
Hence, X = Rs. $$\frac{{100 \times 80}}{{125}}$$  = Rs. 64
CP = Rs. 64
Profit after selling on marked price = 100 - 64 = Rs. 36
% gain = $$\frac{{36 \times 100}}{{64}}$$  = 56.25%