How much percent above the actual price were his article listed?

Step 1: Define variables and set up the initial conditions

Let the Cost Price (CP) of one article be C.
Let the Marked Price (MP) of one article be M.
The dealer makes a profit of 20%, so:
Selling Price (SP) = CP + Profit = C + 0.20C = 1.20C.

Step 2: Account for the discount and the extra articles

The dealer offers a 20% cash discount on the Marked Price.
Selling price of one article = M − 0.20M = 0.80M.
The dealer allows 16 articles for the price of a dozen (12 articles).
Effective Selling Price of 16 articles = 12 × 0.80M = 9.6M.
Cost Price of 16 articles = 16C.

Step 3: Equate the effective selling price to the cost price plus profit

Profit is 20% on the cost of the 16 articles.
9.6M = 16C + (0.20 × 16C)
9.6M = 16C + 3.2C
9.6M = 19.2C

Step 4: Calculate the percentage above the actual price

From the equation: M = (19.2C) / 9.6
M = 2C
Percentage above actual price = ((M − C) / C) × 100%
= ((2C − C) / C) × 100%
= (C / C) × 100% = 100%

Answer:

The article was listed (A) 100% above the actual price.