\(T _1=0^{\circ} C =(0+273) K =273 K\)
\(T _2=200^{\circ}=(200+273) K =473 K\)
\(\eta_1=1-\frac{ T _1}{ T _2}=1-\frac{273}{473}=0.422\)
Case 2:
\(T_1=-200^{\circ} C =(-200+273) K =73 K\)
\(T _2=0^{\circ}=(0+273) K =273 K\)
\(\eta_2=1-\frac{T_1}{T_2}=1-\frac{73}{273}=0.73\)
Ratio of efficiencies, \(\eta_1: \eta_2=0.42: 0.73=1: 1.73\)