A4. The value of Delnici has halved in one year. By what percentage would the value now have to increase to make its price the same as it was a year ago?
(A) 25
(B) 50
(C) 75
(D) 100
(E) 200
A4. If we denote by $a$ the value of the stock before the price reduction, then $\frac{a}{2}$ is the value of the stock after the reduction. Considering the condition, we get the equation $\frac{a}{2}+\frac{a}{2} \cdot \frac{x}{100}=a$, where $x$ represents the sought percentages. The solution to the equation is $x=100$.