A large reservoir at $600\mathrm{K}$ transfers $1200\mathrm{J}$ of heat directly to a large reservoir at $400\mathrm{K}$ through a conducting rod. The entropy change of the universe is

The hot reservoir loses entropy $-1200/600=-2.0\mathrm{J}{\mathrm{K}}^{-1}$ and the cold one gains $+1200/400=+3.0\mathrm{J}{\mathrm{K}}^{-1}$. $\Delta S_{univ}=+1.0\mathrm{J}{\mathrm{K}}^{-1}>0$, as required for an irreversible heat flow. Adding the magnitudes gives $5.0$ and the reverse direction would give $-1.0$ (forbidden).