Final answer:
The price of the stock must increase by 25% to return to its original value.
Step-by-step explanation:
To return to its original value, the price of the stock must increase by the same percentage that it decreased by. In this case, the stock price decreased by 20%. To calculate the percentage increase needed to return to the original value, we can use the formula:
Percentage increase = (percentage decrease / (100 - percentage decrease)) x 100
Plugging in the values, we get:
Percentage increase = (20 / (100 - 20)) x 100 = 25%
Therefore, the price of the stock must increase by 25% to return to its original value.