A number reduced by 30% becomes 280. What percent should it be increased so that it becomes 500?

Question: A number reduced by 30% becomes 280. What percent should it be increased so that it becomes 500?

Solution:
Let, the number be x

Now, x - 30% of x = 280
⇒ x - (30x/100) = 280
⇒ (100x - 30x)/100 = 280
⇒ 70x/100 = 280
⇒ 70x = (280 × 100)
⇒ x = (280 × 100)/70
⇒ x = 400

Required increase = 500 - 400 = 100
∴ Increase % = (100/400) × 100%
= 25%