Let η _ 1 is the efficiency of an engine at T _ 1 = 447 ° C and T _...

The efficiency of an engine is given by $η = 1 - \dfrac{{T}_{L}}{{T}_{H}}$. Here, ${T}_{L}$ and ${T}_{H}$ are in Kelvin scale.

$⇒ {η}_{1} = 1 - \dfrac{147 + 273}{447 + 273} = 1 - \dfrac{420}{720}$

$⇒ {η}_{1} = \dfrac{300}{720}$

And ${η}_{2} = 1 - \dfrac{47 + 273}{947 + 273} = 1 - \dfrac{320}{1220}$

$⇒ {η}_{2} = \dfrac{900}{1220}$

$⇒ \dfrac{{η}_{1}}{{η}_{2}} = \dfrac{300}{720} \times \dfrac{1220}{900} = \dfrac{122}{72 \times 3}$

$⇒ \dfrac{{η}_{1}}{{η}_{2}} = 0 . 56$