-    Let the list price be Rs. x
  80/100x = 24
  => x = 24 x 100/80 = 30        
  ∴ Required S.P. = 70% of Rs. 30
  =Rs.21.

Let the list price of the article be x.

Given, selling price (S.P) of Rs. 24 results in a 20% discount on the list price.

So, the selling price is 80% of the list price.

S.P = 80% of x = 0.8x

S.P = Rs. 24

We can use this information to find the value of x, the list price of the article.

0.8x = 24

x = 24/0.8

x = 30

Therefore, the list price of the article is Rs. 30.

Now, we need to find the selling price that results in a 30% discount on the list price.

A 30% discount on the list price means the selling price is 70% of the list price.

Let the selling price be y.

y = 70% of x = 0.7x

y = 0.7 x 30

y = 21

Therefore, the selling price that results in a 30% discount on the list price is Rs. 21.

Hence, the correct option is C (Rs. 21).

To summarize, we used the following concepts/formulas:

• Discount: Selling Price = List Price - Discount
• Percentage formula: Part = (Percentage / 100) * Whole
• Calculation of selling price using discount percentage and list price.