In 1 st case, Carnot engine operates between temperatures 300 K and 100 K . In 2 nd case, as shown in the figure, a combination of two engines is used. The efficiency of this combination (in 2 nd case) will be :

Step-by-step solution

The efficiency of a Carnot engine operating between two temperatures is given by η = 1 - T L T H For the first case : η = 1 - 100 300 = 2 3 For the second case : η net   = η 1 + η 2 - η 1 η 2 η 1 = 1 - 200 300 = 1 3 η 2 = 1 - 100 200 = 1 2 η net   = 1 3 + 1 2 - 1 6 = 2 3 η (first case) = η (second case)