Using the schematic from Fernando:

$R_1 + ({1 \over R_2 + (50\ \Omega)}+{1 \over R_3 + (50\ \Omega)})^{-1} = 50\ \Omega$

and split ratio

$r = {R_2 + (50\ \Omega) \over R_3 + (50\ \Omega)}$

where $r = 1$ for a 50/50 split, $r = 4$ for a 80/20 split.

Values in his table satisfy these conditions.