The amplifiers X, Y and Z are connected in series. If the voltage gains of X, Y and Z are 10, 20 and 30, respectively and the input signal is 1 mV peak value, then the output signal voltage (peak value) if dc supply voltage is 5V

If multiple amplifiers are staged, their respective gains form an overall gain equal to the product of the individual gains 

Hence $$\begin{gathered} {\mathrm{V}}_{\mathrm{out}}=10\times 20\times 30\times {\mathrm{V}}_{\mathrm{inp}}= 6 \mathrm{V} \\ \mathrm{Since} \mathrm{the} \mathrm{output} \mathrm{voltage} \mathrm{can} \mathrm{not} \mathrm{be} \mathrm{greater} \mathrm{than} \mathrm{the} \mathrm{input} \mathrm{voltage} \mathrm{hence} \mathrm{the} \mathrm{output} \mathrm{voltage} \mathrm{is} 5 \mathrm{V} \end{gathered}$$