A thermodynamic system is taken from an initial state i with internal energy $$U_i = 100 J$$ to the final state f along two different paths iaf and ibf, as schematically shown in the figure. The work done by the system along the paths af, ib and bf are $$W_{af} = 200 J, W_{ib} = 50 J$$ and $$W_{bf} = 100 J$$ respectively. The heat supplied to the system along the path iaf, ib and bf are $$Q_{iaf}, Q_{ib}$$ and $$Q_{bf}$$ respectively. If the internal energy of the system in the state b is $$U_b = 200 J$$ and $$Q_{iaf} = 500 J$$, the ratio $$\frac {Q_{bf}} {Q_{ib}}$$ is