Let the marked price of the article be M.
As per the problem, the article is sold at a 20% discount on the marked price, which means the selling price is 80% of the marked price:
80% of M = 4520
0.8M = 4520
M = 4520/0.8
M = 5650
So the marked price of the article is Rs 5650.
Now, 20% discount on the marked price means that the discount amount is:
20% of M = 20/100 * 5650
= 1130
Therefore, the discount amount is Rs 1130.