2、During the New Year's Day promotion at the mall, the price of color TVs is reduced by $20 \%$. After the promotion, the mall needs to increase the price by $\qquad$ to return to the original price.
[Answer] 25
[Solution] Assume the original price of the TV is $a$, the sale price after the discount is $(1-20\%)a=0.8a$. Assume it needs to be increased by $x\%$ to return to the original price, then we can set up the equation $0.8a \cdot (1+x\%)=a \Rightarrow 1+x\%=\frac{1}{0.8}=\frac{5}{4} \Rightarrow x\%=0.25 \Rightarrow x=25$