The feedback amplifier shown in Fig.has:

Refer to Fig.

Of the four biasing circuits shown in Fig. For a BJT, indicate the one which can have maximum bias stability:

A source produces 4 symbols with probabilities $${1 \over 2},\,{1 \over 4},\,{1 \over 8}\,\,and\,\,{1 \over 8}.$$ For this source, a practical coding scheme has an average codeword lenght of 2 bits/symbols. The efficiency of the code is :