When amplifiers are cascaded in series, the total voltage gain ($A_v$) is the product of their individual voltage gains. Total voltage gain, $A_v = A_{v1} \times A_{v2} = 20 \times 20 = 400$. The output voltage ($V_{out}$) is the product of the total voltage gain and the input voltage ($V_{in}$). $V_{out} = A_v \times V_{in} = 400 \times 0.01\text{ V} = 4.0\text{ V}$.