Carnot efficiency

A Carnot engine operates between $600\,K$ and $300\,K$. Its maximum efficiency is:

According to the second law, the efficiency of any real heat engine is always:

A Carnot refrigerator operates between $250\,\mathrm{K}$ and $300\,\mathrm{K}$. Its coefficient of performance ($COP = T_{cold}/(T_{hot} - T_{cold})$) is: