A merchant marks the price of his article 50 percent above the cost price. If he allows 20 percent discount, then what is the profit or loss percentage?

Given:
Marked Price (MP) is 50% above Cost Price (CP).
Discount allowed is 20% on the Marked Price (MP).
Formula Used:
Selling Price (SP) = Marked Price (MP) - Discount
Profit % = [(SP - CP) / CP] * 100 

 Loss % = [(CP - SP) / CP] * 100
Solution:
Let the Cost Price (CP) be 100 units.
Marked Price (MP) = CP + 50% of CP = 100 + 50 = 150 units
Discount = 20% of MP = 20% of 150 = 30 units
Selling Price (SP) = MP - Discount = 150 - 30 = 120 units
Profit = SP - CP = 120 - 100 = 20 units
Profit Percentage = (20 / 100) * 100 = 20%
Thus, the merchant makes a profit of 20%.