A number reduced by 25% becomes 225. What percent should it be increase so that it becomes 390 ?

Answer: Option B

Let the number be x
Then, x - 25% of x = 225
⇒ x - $$\frac{25}{100}$$x = 225
⇒ $$\frac{75x}{100}$$ = 225
⇒ x = $$\frac{225\times 100}{75}$$
⇒ x = 300
Required increase :
= (390 - 300)
= 90
∴ Increase % :
$$\begin{array}{rl}& =\left(\frac{90}{300}\times 100\right)\%\\ & =30\%\end{array}$$