In an aluminum (AI) bar of square cross section, a square hole is drilled and is filled with iron (Fe) as shown in the figure, The electrical resistivities of Al and Fe are $2.7 \times 10^{-8} \Omega \mathrm{~m}$ and $1.0 \times 10^{-7} \Omega \mathrm{~m}$, respectively. The electrical resistance between the two faces P and Q of the composite bar is