Some goods are sold at a discount of 20%. If the same goods are sold without discount, their price will change by :

1. 25% increase

2. 25% decrease

3. 20% increase

4. 20% decrease

Let the marked price of goods be ₹ $100$.

Discount = 20% of marked price

= $\dfrac{20}{100} \times 100$

= $\dfrac{20}{\cancel{100}} \times \cancel{100}$

= $20$

Selling price of goods = Marked price - Discount

= ₹ $100 - 20$

= ₹ $80$

Selling price without discount = marked price of the goods = ₹ $100$

Difference in the selling price = ₹ $100 - 80$

(∵ Difference is positive means selling price has increased.)

Increase in price = $\dfrac{\text{Difference in S.P.}}{\text{Initial M.P.}} \times 100\%$

= $\dfrac{20}{100}\times100\%$

= $\dfrac{20}{\cancel{100}}\times\cancel{100}\%$

= $20\% \text{ increase}$

Hence,option 3 is the correct option.