A sound absorber attenuates the sound level by $20\text{dB}$. The intensity decreases by a factor of:

The sound level $\beta$ in decibels is defined as:
$$\beta =10{\log }_{10}\left(\frac{I}{I_0}\right)$$
The change in sound level is:
$$\Delta \beta ={\beta }_1-{\beta }_2=10{\log }_{10}\left(\frac{I_1}{I_2}\right)$$
Given $\Delta \beta =20\text{dB}$:
$$20=10{\log }_{10}\left(\frac{I_1}{I_2}\right)$$
$$2={\log }_{10}\left(\frac{I_1}{I_2}\right)$$
$$10^2=\frac{I_1}{I_2}⟹\frac{I_1}{I_2}=100$$
The intensity decreases by a factor of $100$.