Question on Matched 3dB attenuator
You are on the rigth way with the \$41,44 \Omega\$ calculation.

The schematics are simplifications from top to bottom.
For example the middle schematic shows on the right hand side the part from the top schematic that can be expressed by an equivalent R (left side). 



\$R_{eq}= \frac{R_p*(Rs_ + R_L)}{R_p+(Rs_ + R_L)} = 41.44 \, \Omega \$ 

Derivation:

\$1) V_{R_s} = R_s*i \$

\$2) V_{R_{eq}} = R_{eq}*i \$

\$V_1 = V_{R_s} + V_{R_{eq}} = R_s*i + R_{eq}*i = i*(R_s + R_{eq})\$

\$i =V_1 /(R_s + R_{eq})\$



Subsituting i in 1) and 2):

\$V_{R_s} = R_s*(V_1 /(R_s + R_{eq}))\$

\$V_{R_{eq}} = R_{eq}*(V_1 /(R_s + R_{eq}))\$



\$V_0\$ being \$V_{R_{eq}}\$:

\$V_0 = \frac{V_1*R_{eq}}{R_s + R_{eq}}\$

for \$V_1=1V\$:

\$V_0 = 0.829 V\$