The price of an item increased by $20\%$  then decreased by $20\%$ the final price as compared to original price is

Price when increased by $20\%$

$=x\left(\frac{100+20}{100}\right)$

$=x\times \frac{12}{10}=\frac{6x}{5}$

Decreased by $20\%$

$=\frac{6x}{5}\left(\frac{100-20}{100}\right)$

$=\frac{6x}{5}\times \frac{80}{100}=\frac{24x}{25}$

Difference$=x-\frac{24x}{25}=\frac{25x-24x}{25}=\frac{x}{25}$

decrease$\%=\frac{\frac{x}{25}}{x}\times 100=\frac{100}{25}=4\%$