System 1:
Temperature of source, T1=400K
Temperature of sink, T2=300K
∴ efficiency of engine is,
η1=1−T2T1=1−300400=0.25
System 2:
Temperature of source, T1=300K
Temperature of sink, T2=200K
∴ efficiency of this engine is,
η2=1−T2T1=1−200300=0.33
∴ Ratio of efficiencies is,
η1η2=0.250.33=1/41/3=34=0.75